System - I don't mean to be rude but reading between your words it seems your real issue seems to be that the job has become less skilled to the point that almost anyone can do it these days?
Almost anyone with reasonable diy skills can attempt plumbing these days, without having any experience of copper pipe, soldering and with a little knowledge rand a "How To" guide from B&Q many homeowners are tackling jobs that they would have automatically called a plumber in to do for them a few years back.
Whether or not a diy/novice person makes a pigs ear of it, with the advent of plastic and flexies etc, they will attempt it first before even considering getting a pro in to do it.
In my opinion botched jobs by novices using plastic is what gives it a bad name. Used properly and in the correct conditions, it's ok.
It's biggest downfall is that it's subject to rodent attack and the damage it causes. Rodents are present in most households at some time or another and you'd hardly even know they're there. Even in the cleanest of houses, mice will be there. That's one of the reasons I hesitate in installing plastic under a new bath. I've seen many times the damage caused by mice eating through pipes.
Compression is a lot more difficult for a novice than pushfit mate. Even in the hands of a pro, pushfit is far easier to assemble.
And I do welcome progress and new materials and systems, wetrooms being a good example, but in my opinion, not all progress is good.
As for lead, a lead roof properly installed will easily outlast ANY modern material.