Stop making so many champs lvl 50, make more lvl 60 champs instead. The power increase is not linear (not 5/6 to 6/6). Instead, a lvl 60 champ may be twice as good as his own lvl 50 version or even better. You have only three champs at lvl 60 right now, it's nearly impossible to do Doomtower with that.
Don't feed any champs that are rare or above unlike you are really sure you don't need them anymore. You allready know and mentioned that this was a mistake you made.
Open some green shards or buy some random uncommen at the market. Use a campaign farmer to clear campaign stage 12-3 brutal alongside with 3 uncommen champs that get levelled up (Aleks should do for now, on the long run you should use somebody who has more AoE attacks and does this faster). These uncommen champs are levelled only for the purpose of beeing food for the champs you really want to level up. Campaigne stage 12-3 brutal is quite easy to do, gives high exp and silver (sell the shields you get as loot).
The food champs get no ascension and no equip, they get sacrificed anyway.
5 rank 5 champs needed to bring one champ to rank 6.
4 rank 4 champs needed to bring one champ to rank 5 (20 for 5 champs).
3 rank 3 champs needed to bring one champ to rank 4 (60 for 20 champs).
2 rank 2 champs needed to bring one champ to rank 3 (120 for 60 champs).
So yes, it's a lot of repetitive grinding, but unless you want to spent all your money on chickens, it's the way to get champs to lvl 60.
The next champions I would bring to 60 are Scyl (healing, revive, stun), Ninja (one of the best PvE damage dealers in the game) and Zavia (great combination of pure hit damage and poison).
None of the champs you have made lvl 60 so far would have been my first choice, but was is done, is done.
You are far away from completing Doom Tower normal. Take this as a long term goal instead.
After you made the named champs lvl 60, you have a team to beat the Dragon Dungeon, consisting of Whisper (not really good, but she is allready lvl 60, can be replaced as you make more champs lvl 60 later on), Aleks (decrease def on enemies), Scyl (heal/revive), Zavia (Poison) and Ninja (damage).
The Dragon Dungeon is your way to get better gear for your champions. When these champs are lvl 60 and have some proper gear, you can start to lvl up some more niche champs you need for certain Doomtwer bosses, like the uncommen Armiger, who helps to beat the Scarab King.
After this is done, you can think about beating the normal Doom Tower. Even the normal version of the Tower is not early game content.