In terms of players not all being equal, is there any logical reason why this argument would be any different than with regular injuries? It would be bad luck for Palace if Zaha was unavailable, just like it would have been had he broke his leg. As you say, if you agree to restarting during the pandemic then you're accepting that a player could be unavailable due to a positive test. Will it be 100% fair? No but we're kidding ourselves if we think football is 100% fair and equal now anyway.
Pandemic or no pandemic, is it fair on Bournemouth, Watford, Norwich and West Ham that Liverpool are likely to have nothing to play for by the time they play Brighton & Villa, having played us when we were chasing the title? No. Is it fair on Utd that our game with Chelsea will have nothing riding on it? No, just like it's not fair that one side will play Liverpool or City 3 days before/after a CL game and another side will play them when they've had 7 days rest or one team has to play Spurs with Kane available and others with Kane injured.