I actually think there is a legitimate mathematical argument that no LL, FastPass, etc. would reduce lines/waits overall -- it just wouldn't reduce them at headliners.
A 75 minute wait with LL is different than a 75 minute wait without LL from a park ops standpoint, because the latter has significantly more people actually waiting in line (although the fact that people sometimes end up waiting 20+ minutes in the LL line counteracts this to an extent). Since more people would be in queues, the non-headliners would probably have shorter waits by the simple fact there are fewer people available to enter those queues. It would potentially reduce crowding in the shops, QS, etc. as well for the same reason (i.e. that more people would actually be waiting in queues).
But I think it comes down to personal opinion whether that trade-off is worth it.