I am actually beginning to like the Coliseum

the loop is NOT working and they obviously didn't test it enough (if at all). there was a hotfix at the release of both new chars already. it seems that if you paid a bit for luke (like i did, 1 crystal pack both for mats and currency), ig-90 will weaken you unless you pay for him as well (which i think they didn't realise when they released the system).

at low levels the charactes do not have any interesting abilities, so the fights are incredibly boring, which is bad by itself, but even worse if you consider that we are stuck with those characters for a while, some of which we might not care about.

with the old system there was 1 week of marquee and if you did not care about the character, you were done with it. in the new system, you are stuck for weeks with it, cause ignoring it means you lose out on a juicy new currency. this is not a good way to release new material. well, unless... 😉

anyway, the new system need some real reworking. at this point it is not very good. hopefully it will not generate the nevenue they expect, then we might see some changes.

keep the coliseum (bossfights are fun), but also offer it for team testing, not only against bosses, but other players (maybe a seperate ranking with lowlevel payouts?). a few free fights/day, more at cost. this means money for you without seriously unbalancing the game (as any great combos discovered would soon be made public anyway). need more money? give people a way to get different skins. i am f2p, but i might pay cash money to get the old princess leia toon back. the new one, based on that TERRIBLE rogue one cgi-monster? not for me.

do not force people to play to advance through weird, convoluted systems that actually harm our enjoyment of the game. make the game as fun as possible and people will throw their money at you and love you for it!

I think this is the problem I spent some on Luke to experiment and because its anniversary I event. But now I either continue to spend or what I have spent so far is massively devalued in weeks. I am still looking at the same end point of level 65. This is not motivating me to ever spend on the Era again. If I had been given some marginal increase in line with the FTP or IG90 matched my luke then I may of dipped into spending on some further marquees throughout but to erode my progress by the next marquee and slowly let FTP catch up to force me to continue spending feels bad. So I may as well play it FTP in the future.

Yes, that is basically the problem with summons that I described. I think a solution might be to just match the level of new characters to the old ones rather than give a fixed amount of resources from the marquee, but it would have its own set of problems (like an absolutely massive advantage for whales). 
As for other uses for the coliseum, it is the closest thing to an endless mode we have seen so far. Hopefully they add something like that eventually, the framework is already in place and all they have to do is allow different sets of characters. Although the reward structure needs to be changed to absolute numbers rather than relative position in a shard.

The mausoleum is heavily bugged and glitches out A LOT!   It would be nice if they could fix that.    I still hate it, but at least I could make my attempts at RNG semi-useful.     I think the whole thing is complete trash, but I respect your opinion.   It is good that someone likes it. 

Thankfully it runs mostly smoothly for me, I get how that could sour the experience.

ig-90 will weaken you unless you pay for him as well (which i think they didn't realise when they released the system). This is by design. It absolutly intentional.