In actuality, no team has been able to comfortably flex subs out the way SKT has been able to do and it's only as of this split where very few other teams are actually taking that risk without throwing favoritism. Heck even SKT themselves are among those few (especially with them pretty much securing 1st for the RR) and are improving on that from their past season.
The way you word it makes it sound like you disapprove of how well TSM has been able to do with Turtle to not need to have DL on reserve which that in itself was a decision he could have made for himself anyway. And even still, TSM hasn't composed any actual success out of a flexible 6+ team roster as of yet; most teams who have attempted haven't either.