Hey Plarium.. some suggestion
Hey, I am not sure what change you did in arena, but clearly, a lot of players still complains in your matchmaking.
To make it clear, If you don't know yet, players that complains does not want fair matchmaking. They want EASY battles. They don't want to work hard on their account. They don't want to stop in their missions for a while (when I say for a while, I meant is to stop with their missions and do 4-6 months of farming) to farm gear in dungeon. So I suggest, either put all "bot" defense, that will be 100x weaker than the attacker, or change the missions/quest.
I know you don't want to remove Gold 4 as a requirement for Arbiter but these players are salty to the old players who already got their Arbiter. (I mean, honestly, I think that all these players who complain, even you give them Arbiter now and max their great hall, they will still not be able to get to gold 4 as I don't think they have the gear needed to go to gold 4 :D. Even 2 yrs ago, gold 4 will almost always will require you to have at least 300speed turnmeter booster in order to stay in gold 4.)
Here's a suggestion want you can add/change in the missions.
Add /change a mission that will require them to get a champion with a Speed leader.
Add / change a mission that will require them to get a turnmeter booster.
Add / change a mission that will require them to put their turnmeter booster to like 200 / 220 / 240 / 260 / 280 / 300 speed.
Add / change a mission that will require them to make a four man team in arena that are speed sync.
Add / change a mission that will require them to speed nuke an opponent higher than their team power.
The reason behind these add/change in the missions is to teach them to play the basic offense in arena. Since most of these complaining players, does not really know or perhaps they seem that they just can cruise to gold 4 by just playing casually. Teach your players how to play arena tru your missions.
If changing a mission now is complicated. You can just add these as a "Bonus" mission, that is part of the existing missions. Similar to doom tower's secret missions.
Another suggestion is to add champions as a reward that are good in arena. Let's say, after the mission reach bronze 4 (as an example only), they will have a Gorgorab as a reward. Next, is a Seeker. So they can a good speed lead and a turnmeter booster as a mission reward. But remember to put it in earlier missions with very easy task. Because as you know, your players are lazy and always salty.