IIRC Proton is subcontracted out to Codeweavers, who are also known for making a commercial fork of Wine called Crossover (I should mention they're really good

IIRC Proton is subcontracted out to Codeweavers, who are also known for making a commercial fork of Wine called Crossover (I should mention they're really good about upstreaming improvements back into Wine— I haven't looked at the numbers but I wouldn't be surprised if most of the commits in Wine were coming from Codeweavers employees)