Coliseum is a stain upon this game and it is no fun to play. Clearly "fun" was the last thing on their minds. It's not even worth calling it a game mode since you don't really get to play it. You have so few options that there is no possibility of forming a strategy before it locks out the damage and your team is hitting for 1 hp when you need thousands more damage just to reach the next milestone.
It's a gated rage fest of slop. Every time you think you've gotten ahead or cleared the next milestone CG amps up the difficulty exponentially. Upgrading these characters between levels has virtually no difference or benefit the next time you play the run.
To make matters worse. CG made this game mode exclusively for the fact of removing galactic challenges and the ability to play test teams or a way to gain achievements. They don't even give us options for who these characters are good with. We're just supposed to guess what team they go on or read their ability descriptions for references to other characters. CG doesn't want us to have fun with any of these character and see their full potential on a proper team with synergy. This is just the most lazy unfinished garbage we have ever seen so far.
I don't care that we get to unlock any of these characters for free at the end of the era. I have no interest in any of the characters while using them in Coliseum. It's not like we get to fully unlock them either when they still require stars to be farmed at a much later date. I hate everything about this sloppy lazy excuse for an event that greatly takes away from the game and the drive to want to play it.
I have been playing for over 10 years and have spent money on a few things in the past. Nothing is even remotely worth spending on these days. CG likes to play their tired out gimmicks to get all the fools to part with their money for nothing in return. Somehow it's working out really well for CG, so they couldn't care less about what the people who have kept this game going for the past 10+ years think.