You know that moment, as a developer, when you realized you never really took into account how to scale your game so you compensated with requiring in-game purchases to make up for your inability to create a reasonable algorithm? Yeahhh...
One suggestion is to persist the gold/key bonuses after reincarnation. Another is to persist the bonus to a hero upon hitting level 100. These don't carry over into reincarnation so the game doesn't really go anywhere.
Game doesn't scale very well. 5 reincarnations and it's not worth going past level 100. Almost no benefit to spending money on lower heroes. The idle game doesn't scale at all. The bonuses only apply to clicking. You have a decent concept, but math is killing you.
Can you send a personal note when the end game is balanced? Like the game and the balance up to that point was pretty solid. you actually had to think about what to focus on. Good game and happy to come back when it's ready.