Right, and unlike wings, bigs can passively provide value at the basket whereas perimeter players cannot. I don't think it's clear cut that a stretch 5 provides that much more value (if at all) to an equivalent rim running/offensive rebounding big. Sometimes you get these bigs hanging around the perimeter all game and the actual effect is that you just get a mediocre shooter.
Eh...Is that the magic of a stretch 5 or is it simply having good players? The bulk of Chet's offensive value, for example, is his ability to create shots around the basket and convert them at a very high level. His shooting obviously opens that up a bit, but if he couldn't shoot a 3 pointer, he'd still be a massive factor for OKC. If you kept his shooting, but took away his ability around the basket I don't think that jump would have happened. Likewise with BOS, Porzingis is an awesome shooter but he's just an awesome player in general. Had it been Gobert going to BOS, I think BOS would still be as dominant as they are. Chet and Porzingis are both great players, any team that adds a player of that caliber (without losing talent) is going to see a huge jump.
I do think it's a big bonus if a C can shoot, but I do think it's gotten to a point where it's overvalued. I guess this really comes into play when you have multiple non shooters. Like I don't think Giannis/Porzingis is the same as Giannis/Gobert. So while that definitely has value, I think the extent to which it is valuable has probably been overstated.