It will be cool if Apple opens the browser and app installation options allowing PWAs to run like iOS Apps (and all the people working with web apps will be happy).
My biggest concern with PWAs is that only ads are a viable business model for small utility apps.
The App Store rules are terrible (and give Apple too much power). But, it allows selling small utilities. In a world of PWAs, your monetization options are subscription, donation, or ads.
A subscription for a small tool doesn't make sense. Donations don't scale. Hence, the most probable option will be ads.
I agree with you. Having Safari as the only option for iOS is anti-competitive. But, honestly, the competition (Google) will love to have a world of apps relying on their ads infra. The first thing I'll do if I were Google is to add all the missing APIs to Chrome PWAs, so devs don't have a good reason to continue using the App Store. I don't love the idea of having ads and tracking in every little app.
I always find it interesting that Facebook and Google get trotted out as potential boogeymen whenever the topic of greater consumer choice on all computing platforms is brought up, because such arguments conveniently downplay the very real and actually present enemy to user freedom that is Apple literally dictating what products consumers are allowed to use on their own devices.
It's not about competition in browser choices as an iOS user. I'm talking about more diversity across platforms, as opposed to a single engine everywhere, and especially about who'd control that engine (if the single engine was some FOSS one, created by strong community or cross-industry collaboration, I'd might be ok with that).
So, iOS being Webkit only, means it's still more competition than Chrome/Google dictating everything about the web, and taking it into whatever direction it pleased it.
At least now websites NEED to be compatible with iOS, and Google still needs to at least somewhat pretend to care for web standards, and it also means whatever Google unilatery pushes as a new web API or feature doesn't just get adopted by everybody.
Safari would still be big on iOS because it has some very useful features and integrations that the competition doesn't offer. Apple's pseudo-TOR and lockdown mode are just two examples from the top of my head of things the competition isn't putting too much effort into. Microsoft has super-duper secure mode, but I don't think Edge users really care.