I was able to finish it by speedrunning in the end. But I checked out the chrome inspect log when the game was stuck, it showed a reference to https://bugs.chromium.org/p/chromium/issues/detail?id=1144736#c27 Maybe it could be helpful to devs.
Spoiler - Easy BoTD TACTIC:
Okay, figured it out and tested now. It works without even prestige bonus. The key here is that blessed is kind of OP. Play the game normally until you buy blessed for Cleric. I also had warrior damage taken (1/2), it helps but I don't think it is required for the tactic.
Next up, following tactic gives you BoTD (ie: medium badge/100 floors)
My build was 1 warrior max hp in front. as many clerics as possible (4 in my case) with max healing, 1 ranger but with MIN damage, basically with a single damage stat and rest unspent. (If I didn't put at least one ranger, clerics started attacking instead of aimlessly healing. By adding a ranger we force them to heal constantly, therefore buffing everyone infinitely with the blessing)
That way, I was able to get from floor 1 to 100.
oh realized, you don't even need warrior damage taken,
I think the easiest way to get to level 100 is first get blessed for cleric. then put 1 warrior with max hp, keep the rest as clerics with max healing. You probably won't even need to prestige afterwards.
The mege ratios are
3->1
5->2
9->4
17->8
ie: 2^n + 1 -> 2^(n-1)
Our lives would've been much easier if the dev chose:
3->1
7->3
15->7
31->15
63->31
ie: 2^n - 1 -> 2^(n-1) - 1
That way we wouldn't need those extra ones to be merged to level up to top :(
can't get any in-game achievement for some reason. I've finished the journey but non of the in-game achievements are unlocked. Thus, I cannot get the second medium badge
 "That Pokeyman Thing Your Grandkids Are Into"){kind=icon}
 "The Evil Lair"){kind=icon}
 "Incremental Adventures"){kind=icon}
 "Tropical Merge"){kind=icon}
 "Accelerator"){kind=icon}
 "Flight"){kind=icon}
 "Words and Physics"){kind=icon}