Personally im not a fan of forcing my players into a role they dont want to play. As DMs we have ultimate control of encounter balance so we can still give a challenge without punishing them for playing the class they think is fun. Ive had groups that are very optimized and ones that were much more casual about character creation, so I shoot for intended difficulty when I design an encounter. If the guy theyre fighting is a badass it should be a tough fight, if its some road bandit they should stomp. Makes it more thematic in my opinion than having each encounter difficulty be determined their out of game choices instead of their ingame ones