I don’t think that’s fundamentally the question at all. This is a classic example of over reductive.
What is even a “primary offensive weapon” in 2020? Most great teams have multiple. Was Shaq or Kobe the primary offensive weapon? Does it matter (No.) Was Steph or KD the primary offensive weapon? (It doesn’t matter even though some stupid people still argue about it). Was Tim Duncan, Manu, Tony Parker or Kawhi the primary offensive weapon? At different times they all were... Who is the Nets primary offensive weapon this year?
In terms of the actual game, it’s clear that Giannis shouldn’t be the primary ball handler. As far as the “primary offensive weapon” the reason he isn’t is because they need at least one additional primary offensive weapon to win a championship. Can he be one of them? If the talents are complementary, absolutely.