5 subs is stupid. 3 subs were far better. Now, you can replace half the outfield players, which basically means you can change tactics completely. It means more of the result is down to the manager. It also means there’s less need to prioritise which games are important, you can start with your best 11 every game, and just substitute later if the result allows it. It also benefits clubs with bigger budgets more, as they can afford having a higher quality bench.
I don’t see how a salary cap could possibly work globally, and if it was introduced on a local or regional basis you’d just drive more players to other places.
I also suspect that UEFA do SO much to appease the “superleague clubs” they would never approve it.
May also be against employment legislation in lots of places
It only works in the US because the teams are franchises and the players are contracted to the league itself (correct me if I’m wrong?)
But if you can convince me it would work, I don’t necessarily object…