I play an alchemist in an age of ashes campaign and I've DMed a plaguestone campaign with many NPCs focused around alchemical items. I think that if you spend too much time on reddit that it skews your perspective towards a bunch of theory crafting. Alchemists have great roleplaying opportunity, great crafting options, and great versatility. They won't ever be the best at anything you set out to do but my god if you need to do something in a pinch you've got an elixir for that. Wanna see in the dark better? We got a potion, put down the torch. Wanna be more resistant to disease? We got a potion. Sheild's busted up? Let me repair that. -2AC on a standard attack with shocking alchemical attack? Bombs away with bottled lightning, Yep we got that.
Alchemists fill a variety of needs from healing, damage, buffs, and debuffing.
I can't speak to mutagenist but i think Chiurgeons need some attention though with a minor clarification. I believe that if the crafting skill use for medicine feats were clarified to make every medicine feat available via crafting training/level then I think that would be the best way to proceed. I will homerule that it is as intended for an alchemist chiurgeon because I think it makes viable to be a chiurgeon healer for the party. I think there are some people running mutagenist tank successfully, but my knowledge is limited on that.
Overall I think the power level of the alchemist is above average, and the versatility is outstanding, but having a frost vial, a fire vial, and a quick alchemy action to make anything else you need for a fight doesn't play out well in the math.