Im not sure I’m following what you are after, if PWAs work for you, why would you want an alternative? Nothing bad about them -apart from memory usage maybe-.
Some food for thought.
1.- Use something like Rambox/Franz/Ferdi/Biscuit.app to embed your most used web apps. This is a crowded space so it’s not difficult to find a lot of alternatives.
2.- Use a solution inside the browser. I find Orion’s vertical tab groups & windows very intriguing, but maybe for your use case you just need pinned tabs in Safari, always a shortcut away. Another similar option is Vivaldi, that can embed any responsive web app in its bookmarks & history sidebar: its kind of a kludge but works, you can set the width of the window to be used for this “app on a sidebar” and also set a keystroke.
Alas, with these two approaches you lose the global app switcher, of course. Maybe a third one could be dedicated Spaces for different browser windows?
The question I have is what problem are you trying to solve?
From the other string, I wonder if it is that there are problems with memory. So is your issue that you are having memory issues?
If not, and the PWA apps are working for you, and your post gives a number of benefits you enjoy, I’m not sure I understand what the reason for replacing PWAs is?
I too find the benefits of ‘web site apps’ to be quite useful. @ThatNerd suggests a command line tool to great such ‘apps’. I use Unite to create such apps (although if I had known of the command line tool I may have gone with that).
(Now my Studio has 64 GB of RAM, so I’m not experiencing memory issues).