One thing I noticed about both Google and Facebook’s apps before deleting them was that in addition to using more battery, both were slower in their apps than using the web site. That was surprising but consistent & a large part of why I ditched them.
Well, I believe you can do that if you pay for YouTube Extortion Edition or whatever it's called. Which I used to do, until too many ads still came through and I got pissed off.
(Though note: if I got to a YouTube link through anything other than going directly to the site and searching, then it would open in the app. Which would then pause when I turned off the screen. Which was irritating. Fixed by disabling the YouTube app entirely. Life is much better now.)
Which performance concerns?
A lot of the examples I’ve seen were unexpected situations: e.g. if you look at every <img> with a poorly-tuned regex and someone uses data: URLs, it might be backtracking pathologically on orders of magnitude longer strings. There used to be an issue with each injected CSS file being stored separately - it was fixed years ago but there was a multi-year period where people would complain about Firefox being slow, you’d ask if they had AdBlock Plus installed, and the performance issue cleared up as soon as they disabled it – the problem was an extremely large style sheet multiplied by every open tab and iframe. It was bad enough that they officially called it out on the Mozilla blog:
https://blog.mozilla.org/nnethercote/2014/05/14/adblock-plus...
The other thing to remember is that a browser developer has to support every user, not just the savvy ones. You might know to stick to certain more-trusted extension but the Safari developer’s threat model has to include someone’s grandfather installing McEaglePatriotGuardElite and blaming Apple when their iPad is slow or that injected code is exploitable. Apple characteristically chose to respond to that by reducing flexibility, which is certainly a valid decision but also one people can reasonably disagree with.
And what would those be? When this question is asked, people inevitably bring up Twitter as the shining example. And it's just horrendously bad.
Don't get me wrong, a really well-written PWA with fully cached assets is often almost at a native app experience level, but that's not usually the case with most mWeb implementations.