It's not the size, it's the strength of the back-up players isn't it? When City's first team are tired they can bring on 5 more world class players who are all being paid 100 grand a week. If the likes of Sheffield Utd or Burnley are making 5 subs then they're bringing on Championship players essentially.
It could also help player development with more teams bringing through Youth players
It’s an extra potential two players to come with a match day squad increasing to 20
Apparently 15 managers out of 20 are now in favour where as before it was 11 in favour
The EFL allow 5 , CL allow 5 - so why not the Prem.
Clearly people will look at their own teams and judge from the size/quality of their squad but we for example would be using a lot more youth and academy players