have you flown with a range of PPLs recently and asked them to demonstrate a PFL without warning?
Haha! I do! It's amazing what you can get away with doing to another pilot while you're doing type training or a test flight! I do lots of PFLs, as I shut engines down in flight a lot - so far they have always restarted.....
What I see here is an odd triangular argument. Some argue that a BRS is needed, to be the most safe under the circumstances of most engine failures. This presupposes that these people think that engine failures are common (I'm not expressing an opinion right now). Others are saying that engine failures are really quite rare, and this is a low risk, thus not requiring the safety benefits of the BRS. Then others are saying that most PPLs do not maintain proficiency in PFLs, which they should be doing.
If engine failures are common enough to pose a real safety risk, this would be evident across all GA aircraft, and PPL's (and a whole bunch of CPLs too!) would simply be scared into regular PFLs. That does not seem to happen - evidence the agreed lack of PFL proficiency. This could be interpreted to mean that pilots think that the engines are pretty reliable, and forced landings are uncommon.
So why do we need the cost and weight of the BRS to mitigate engine failures?