It’s rather obvious though that people prefer to upgrade a character which they like rather than some random 5-minute character, plus if they are very good in the game even more people will be interested.
And with stamina issues some players might not upgrade character which they like because it’s just waste of their resources and would keep using characters which they have already maxed.
Some players don’t use any media around the game like the forums or discord, they end not knowing who is good when the new character drops and blindly upgrading heroes, once they discover the truth they might stop upgrading that hero and completely abandon them.
Again, 6000 diamonds isn’t that good nowadays, unless there will be some new source which will allow to use diamonds on something good.
Like Event Crate which can give CW resets, disk power, mission speed-ups, tons of red skill chips… or give these to hero quest rewards.