I don't think multiclassing is weak in 5e , apart of minimun attributes that we usually ignore at my table. (We usually roll so it has no sense for a player to whant a specific concept like sorcerer paladin hexblade and not be able to do it couse it didnt roll enought str).
Still, most of my players dont do multiclass, mostly because it needs a lot of game knowledge to do right, and MOST of my players dont like to spend so much time with it .
But there are other players that do ... vengance paladin, warlock, phoenix sorcerer combos for twinned greenflameblades with smites and so on .. and I did a warrior/ ranger/roque that could be permanently invisible while doing 600+ damage in the first combat round at lvl 11.
what build of fighter/rogue/ranger can be permanently invisible and 600+ damage in the first round?