Allies as bad story-telling

Funny enough, they prove your point in game for at least one mission. The BoP Lexcorp tower solo instance has Superman help you up to the point you meet Ivy, then he has to leave to save kids in a bus that is going to fall off a bridge. He then shows up at the end for as long as it takes for the both of you to beat back Lobo.

(Long stupid idea below, you were warned.)

Then again, the way they could get around giving the players variants of the Heroes / Villains as replacement sidekicks would be have our players make a robotic / magical sidekick that unlocks abilities / quarks/ identities/ syles of said iconics. Instead of Batman, get a super powered Bat bot that mimics Batman. Wonder Woman and other magical sidekicks could be amalgams that are summoned. Each version of the iconics could use their weapon setup and gadgets so as if you were partnered with them like you are sometimes in Solo/Duo missions.

All the points and allies we have access to now could be converted into chips / runes that we slot into the bot to give it more abilities along with unlocking passives. Maybe even set it where each time you max out an Alley chip/rune, the passives stay active even when switched out, so in the end if you max out all of them you will have one hades of an omni-bot. Maxing them would also let you swap out parts so each player bot could look different

As for the FoMo iconics, they could set up "generics" that allow for their abilities until you finally get them, at which point the generics are sacrificed and the levels are transferred over.

One interesting immersion idea would be an instance where your allies are disabled because they have been captured. As you progress through the instance, you find opportunities to free them and get them back one at a time.

I think that may be too technically complicated for group content, but could be a good idea for a solo just to shake things up