Suggestion: to reduce duplicates, grant an automatic ascension to consumption of a duplicate 4 or 5* hero. I know the ascension materials are supposed to be rare, but so are duplicate 5 star heros. Example: I have 2 horghalls, which won’t get leveled because I don’t have the mats. But if feeding one to the other would give me the 3rd or 4th ascension, I’d definitely put him on a levelling path. And while SGG would lose the gems from increasing our hero caps, they’d definitely get more from people spending on summons.
Why not use hero academy to trade them in instead?
That would be wonderful for those of us who have HA10. For those (including, full disclosure, myself) who do not, it would allow otherwise unused 5*s to get some action while allowing people to level and build up their strongholds. HA10 would, under my theory, still retain value – there are lots of people who would prefer a HA10 retraining of Quintus to try and get Hel or Gravemaker rather than just consume him to get a next-tier Quintus. But I’m also looking at ways to attract/retain new and midlevel players who might otherwise be discouraged at attaining HA10.
Hero Academy level 10 is slow too…a week per transaction. I’ll never get rid of my dupes and 95% of what you get from HA10 are dupes too.
I currently have 63 dupe 5* heroes who have not and will likely never see a single level up. HA10 is a nice feature but doesn’t do much to my glutton of dupes. And to the OP’s point, eating them would be a waste, too.