Drop IG90 from Coliseum?

It seems crazy, but yes based on my experience the past two days.  I have Luke at 21 and IG at 20 and still got 7% higher without IG today.  I even tried a run with IG as lead and still was worse than without him.  It is making it really difficult to advance at this point.

I read people advising leveling up only Luke and going in the Coliseum with him only. Others say to level both together (and future era characters). The problem is that once going for a strategy, we have to stick with it till the end. But no idea how Coliseum battles will be once we have full characters set. And also will the Era challenges only be with the newest released character or with all of them

i did things with just luke till ig90 was at the same level 

There seems to be enough resources to level up both, so there is no harm in doing it (how it will change with more characters remains to be seen). The problem is currency, but there is awfully little of that for either strategy. At least it's relatively cheap...
And another thing is that we get fewer summons as we progress though tiers. It will be necessary to level up other characters at some point. All in all, the whole summon system needs a rework. Maybe base it on the high score rather than character levels? That sounds like a fair solution.

This is the big issue, nobody knows, there's no explanation, when it comes to levelling up these Era characters we're all just floundering in the dark.

In Coliseum, summoned units are scaled to the era level of your lowest level character. Just how like raids have unique event modifiers, so does Coliseum. The game mode states this mechanic in the event modifier "Now There Are Five Of Them." This is visible at the bottom of every boss description in the Event Info tab, and when tapping and holding the enemy abilities beneath the boss health bar during an attempt in the coliseum. 

If I go in with Luke alone, I still only get 3 out of the 4 potential summons. Not sure why that changed - is it because we now technically should have 2 characters? Probably. Will it reduce further? Probably?

My Luke is 18 and Iggy is 16. Luke alone I got to 16%, but with both of them I got to 22% (vs Zeffos)

Now the question is, if I had put all of those Iggy resources into Luke instead, would I do better with Luke alone and the 3 stronger summons? Against the Zeffos maybe, because Iggy messes their Armor Plating up with his counter attacks.

Would that harm me once character #3 is released? Will the summoned toon number decrease to 2? At some point I would assume a sole beefy Luke is not better than a bunch of more mediocre toons.

I don't know, and I'm glad it doesn't really matter, because I don't expect to get any big reward at the end of the Era anyway.

If you are planning on u locking Spider-Maul then you need them all at level 45.

In early tiers I think there is an advantage to going with just Luke but later on you will want them. It’s not likely that at early tiers going with just like is getting you to a higher daily rewards bracket so it feels like a better idea to try to level both at the same time. We will get more and more mats upon each character release so that we can try to keep them all at about the same level.

each tier reduces the number of summons