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.
4 subs is optimal IMO, 5 is too much, it’s like fielding a new team
I can agree if the fourth sub is only for the GK.
But I do like to see an outfield player donning the GK jersey. It’s rare, and should remain rare, but it should be a possibility.