And tubular don't benefit as much as clincher when on a super wide rim, they don't get rounder and a little bit larger
Clinchers don't get "rounder" no matter what rim width you use. This is a common misperception; maybe it comes from people thinking of their car and (some) motorcycle tires, which are designed with casings stiff enough to force a non-round cross section. But those tires' construction is radically different from that of bicycle tires. For one, they're almost all radials, while all modern bike tires use bias-ply construction (even Maxxis' Radiale).
All bicycle tire casings (clinchers and tubulars alike) assume a circular cross-section (with a constant radius) when inflated. High-quality bike tires are pressure vessels with extraordinarily supple (flexible) walls. They're all round; their inflation pressure forces them to be round. On a clincher, changing the rim width changes the radius of the casing arc, but it doesn't change whether it's circular.
Some people wax poetic about "round" vs. "lightbulb-shaped" tires, but both kinds of tires have round cross-section casings. Road tire designers can alter the shape of the tread rubber a tiny bit by playing with its thickness, but the underlying casing is round.
Mountain bike treads can have a non-round cross section even though the underlying casing is round. In extreme cases (e.g. A 2.1-inch tire on a 40 mm-internal-width rim) the casing can assume an arc that puts the cornering knobs in the "wrong" place, but again, the underlying casing is still round (it has a constant radius across its section).
I believe some of the old Schwinn "krate" kids' bikes from the '70s came with "drag tires," which were old-style clinchers with enough rubber at the edges of the tread to create a squared-off profile when inflated. But these are hardly comparable to modern racing tires.