You need poisoner for CB. I love Brawler, some say Banshee is better. Brawler needs 0 books, better not to book. Banshee needs like 15 rare books.

Main thought: you seem to be focused too much on sets for your gear and not enough on the stats involved, which could potentially mean that you're underperforming in things like speed and accuracy - which would explain your lack of progress in arena despite having immensely powerful champions. Though that's just a guess and I could be wrong of course. 

Apo, RT and Thenasil are all excellent support champions. To progress in dungeons, you'll probably need to find the right balance between them and your primary group of more attack-oriented champions. And yes, you'll need to take at least some of them to level 60, though often support champions can keep doing their job at level 50 for quite a long time. 

Regarding the other champions you list, the most important ones are obviously High Khatun (at least until you get another champion with a better speed aura) and then either Frozen Banshee or Occult Brawler, opinions are divided on which has the edge overall. Either FB or OB should always be on your clan boss team because poison is so powerful on CB. If neither is developed yet, FB is probably easier since she's a rare and those books are easier to come by. Those will also need to become level 60 eventually, though my FB works fine up to Brutal at level 50. 

For arena, um, you absolutely already have the champions for a strong speed nuking team that could easily get into gold. Ghostborn just might be the single most useful champion out there for a speed nuking team, considering that he puts an unresistable decrease defense AND at the same time increases attack on his own team. Of course booking him to get it to 100 percent would be even better, but still. 

First of all, my apologies for all of the typos. My free time is somewhat short, so I don't always proof read to the best of my abilities. 

To respond to your inquiries:

Trips: I agree that a poisoner is needed. I know Grappler does Poison, but it seems FB and OB do a better job. I am now tempted to start investing in OB as an eventual 60, especially I need to do this for a spirit champion and I have to finish that last challenge where I upgrade a champion to 6 stars (I missed this when I upgraded Ghostborn). However, I would have to take RT out of the rotation since she would constantly cleanse him. 

I agree that the arena has no synergy. I went back and forth with HK or MM in the lead and opted for MM. My hope was that with shield gear he would keep everyone alive the first round, then Sinesha could keep everyone alive with her A3 and then Turvold could pick everyone off. Probably not the best strategy. To answer your question, Apologies is sitting at 196 speed. GB is at 170. HK has been stripped of her gear, so I couldn't give you a reading.

L9753 - I think you have a point at the fact that I could be underperforming because I am going for sets instead of stats. I can rummage through my gear and see what might work better. However, most of my gear that is consider good is either 4-5 stars that have been leveled to rank 12. I am just now starting to get into the phase where I am collecting 6 star gear. Obviously, I need good gear to get great gear, but I am trying to make wise choices. I often find that I will get good gear with decent substates, but I will then get bad rolls as to what gets upgraded. 

I agree with you regarding poisoner and keeping some of the supports at level 50. It's something to play with.

I recognize I do have a potential for a nuke team, but I feel like I am really lacking a nuker (like Kael). Perhaps the answer is to swap out what you suggested and then modify the gear like you also suggested. Sinesha A1 has been lacking, so maybe I need to switch out her retaliation gear. Again, I need to experiment some more. 

Thank you for suggestions and your help. I would love to hear additional insights if you have them (or anyone for that matter). 

Your core 6 are all great champs and will hold you in good stead going forward but for now I would strictly do use on levelling and gearing champs for CB.

CB is the most important area of the game for mine if you want to continue playing without spending a ton money, i’d level your occult brawler in LS gear if possible or frozen banshee which I use myself and is worth the 60  She’s also great for dragon so you’ll find use for her there as well. You’ll want to find an atk down champ as well so I’d priories acquiring and ranking one of those, tender has the lesser version on her A1 but that won’t cut it at higher levels

Apothecary and tender I both use in level 20 dungeons and are both awesome champs but don’t necessarily need to be ranked to 6 star unless you’re going to use them in CB or need some extra stats from the banner, I recently put tender at 5 star into my D20 team and she bought me down to 2:45 purely because of what she offers and what it allowed me to do with my team comp.

You seem to be missing a little crowd control in the way of a AOE atk down or an AOE stun for the trash mobs at higher level dungeons so you could possibly solve that by putting sinesha in a stun set and you also seem to be missing some decrease turn meter champs for both FK and the slider so I’d keep an eye out for those when thinking about future rank ups.

I’d get your HK to 230-240 speed if possible and use her, ghostborn, MM and then turvold In that order as your arena team as that seems to be your best set up and synergy. This would be dependent on how quick you could get the rest of your team running though as you may need apothecary in there to further boost your team or may get get turns interrupted.

Check your vault for the rare coffinsmasher. Perfect atk down for CB. Surprisingly useful in dungeons except for spider. 

And I agree with Liam on the arena advice. Speed is king in arena, especially at lower levels. Though I am starting to think a RES/DEF strategy may work, but would take too long for me to build on my alt. For you HK is probably needed in one of the combos Liam suggested.

I think Apothecary & Brawler at 60 may even take you to Dragon20.  Speed is key in dungeons, Brawler can get 10 poisons up quickly on the dragon and do most of the damage needed himself.  MM needs to be well geared to both stun and tanky enough to survive his ally protect.  Again, I am not sure which is better overall, Brawler or FB. I would think Brawler is easier to build tanky as HP based. The other 2 benefits are 1) no booking needed and 2) His primary posion has no affinity disadvantage.

I think you are right and I will make Brawler and Apo my next 6 star champs. I still need to modify gear around to make my champs stronger. It looks like going for set bonuses (at least with the gear I have) is causing MM and Turvold to underperform. I will re-gear them and once I am done with my current XP Bonuses, I will start hitting the dungeons hard.

My only complaint about Brawler is that there is a lack of synergy with RT. However, it doesn't seem like that this is TOO much of an issue because it's Brawler's A1 and his passive that seem to be more important on CB than his A2. RT will be cleansing him, so he won't be able to effectively use it when it's up, but, again, I think poison application is more important.

I don't currently have any other attack down champions, but if I did, they would probably not be 6 starred anytime soon.

Arena has been better since I modified gear. Now it goes HK, Ghostborn, Turvold, MM. With some modifications, I think I can get MM to go ahead of Turvold and have his A2 be a much stronger nuke. However, I am still finding I have to still be selective in my match ups. This is due in part to not knowing what every champion does, so I don't know who to always target first with Turvold. In general, there aren't a lot of match ups where I know I will automatically win, but I guess that's the name of the game.

Now hope I eventually pull a Coldheart so I can have a chance in Fire Knight's Dungueon.