An experimental period will kill the MCU. People watch capeshit for low risk action films with bland humour. Not anything that will make them think or feel anything besides a momentary high, I have no doubt they'll try at least once to ape Joker and will completely miss out on it's whole points and fail miserably.
I also doubt X-Men will do well, Dark Phenoix seemed to flop, Hugh Jackman will stop playing Wolverine and restarting the franchise again for the third time will just make the audience not want to even bother.
As for the remaining heroes, you are right that Marvel struck gold with low importance heroes (though I don't think Iron Man can be considered that unimportant) but it had time to develop the characters (mostly) with solid films and excellent casting. Outside of Spiderman, I really doubt any other Marvel character that level any build up and following (especially after they nuked any good will towards the Guardian of the Galaxy).