I tihnk you'll genuinely notice it now being the case as it's been pointed out. Refs, atrocious as they might be in calling decisions at times, have a far better knowledge of the laws than pretty much any fan and a lot of players.
It's not a full proof solution, as you point out in your first paragraph, but it's more to do with the idea that if you're wanting to waste time and bring on a physio, you know you're leaving the pitch for a spell. It does stop time wasting.
Generally, even if it's an accident and a player is seriously hurt, the opposition player is usually booked for it due to recklesness.
There's a few anomolies in it but it's certainly reduced the time that players use the physios generally for innocuous "injuries"