EDIT: Apologies. Updated with a link to what gorhill REALLY said:
Manifest v2 uBO will not be automatically replaced by Manifest v3 uBOL[ight]. uBOL is too different from uBO for it to silently replace uBO – you will have to explicitly make a choice as to which extension should replace uBO according to your own prerogatives.
Ultimately whether uBOL is an acceptable alternative to uBO is up to you, it’s not a choice that will be made for you.
Will development of uBO continue? Yes, there are other browsers which are not deprecating Manifest v2, e.g. Firefox.
I use a lot of extensions for a lot of various reasons. Privacy and ad blocking are only two of them. For development purposes, UI preferences, making common actions easier to access, disabling website features I don’t like, re-enabling ones I do, the list goes on and on.
I’m a bit confused about your app vs web comment. What I’m saying is that instead of allowing the web ecosystem to evolve at an organic pace by keeping up with the rest of browsers, apple puts their thumb on the scale, choosing not to support things, so that installing an app works better. This isn’t a matter of comparing ways of building a downloadable app, it’s a matter of them guarding against users quickly accessing a web app without needing to download something from their store (which provides them with profits). They even make money on free apps now!
The entire state of the web is held back because iOS is so popular, and Safari is always behind on feature support especially on iOS. And it really irks me. Many times every browser we support will support a really nice feature, except safari. And sometimes even the latest safari doesn’t support something even though the others have for years!
You are lucky not having to support old versions of Safari. The latest safari is always somewhat reasonable to support but Jesus… try supporting anything of complexity on iOS 14. So painful.