Have you ever won with barbarian or warrior without at least 12 in both Dex and Int? (not that I don't think that multiclassing should be a thing but your no longe truly a fighter once you add INT into your build, you're more of an arcane knight or something)
All classes always take multiple different attributes, that is not what I would call multiclassing. I go 14 str for talents, ~4sp, then int for more damage. As I don't full clear, that is usually around 12ish int, depending on the items I get. For talents, I stick mostly to the base talents, picking up a few barbarian melee abilities. I don't take spells on melee (not that it would be bad), and only occasionally take a passive (shroud of wind for the levitation, stealth mastery). I also don't take duelist abilities on anything other than duelist, as I like the game to not be completely free (I think duelist is absolutely OP).
Here is a typical warrior build for me: https://imgur.com/a/QiPxdbs
And a barbarian build: https://imgur.com/a/DgZvzeA
Warrior run from today - I get int just for the extra damage on the melee abilities: