Mutliclassing in 5e is a half baked optional rule, the land of broken (mostly very underpowered) combos. One good reason for Larian to avoid it is it gives players without 5e system mastery a whole lot of trap options to fall into.
Add an option to respec a few levels. Problem solved.
Respeccing class is definitely not in the PHB! Subclass respecs are, but are not a solution to this.
Also, it's already possible to make a Tav build that sucks. Make a wizard with 8 Intelligence. A Sorcerer/Cleric with rational ability scores will be better than that Easily.
Sure, that is why the game tells you how to allocate your ability scores based on your class selection. It's possible to create a wizard with an intelligence of 8, but only if you do the exact opposite of what the game tells you. It's not possible to do it by accident out of ignorance. But it can't tell you how to allocate ability scores for a multiclassed character, since it doesn't know what you have planned. The PnP rules try to help players by sticking a 13 minimum on the class's main ability score, but that doesn't do enough. I have a monk/wizard multiclass in my current campaign. The only way to balance encounters is to treat that character as if they where a level lower than the rest of the party.
