Thats not true. You can absolutely use HTML 5, Javascript and all the web technologies and develop a web app. Any user can add an app like that to Home Screen and use it like a regular app (Only catch is it will need an internet connection). HTML 5 is completely open and based on common standards. If HTML 5 standards specify Camera access, then iOS provides it.
What you cant do is use Apple in-house built technologies like Xcode, Swift, Apple's iOS API's and other Apple developed technologies for free and develop an app and distribute it without paying Apple a cut. That I think is fair. Sure Apple's technologies is far superior to HTML 5(which is an industry standard), that's what Apple worked hard for. Asking for these technologies without paying Apple anything is unfair.
Technically this is true... up to a point. However any web developer worth their salt knows full well that Apple have gone out of their way to make building web apps as problematic as possible.
Firstly they refused to conform to "common standards" as you put it for progressive web applications (which every other device maker readily abides by) and instead uses proprietary meta tags instead of the approved JSON manifest format. No big deal on the surface I guess but when you throw into that Apples outright refusal to implement several JavaScript API's because they would give web apps capabilities that native apps have (and thereby drive traffic away from the store potentially) and also their refusal to correctly follow the ServiceWorker standard agreed upon by the W3C which means web apps can't cache correctly or work offline properly then all you end up with on Apple devices is a webpage that looks like an app - not a web app.
At present there are only three active browser engines:
Blink which powers Chromium, Chrome, Edge, Opera, etc - Supports the most web standards and is actively worked on by Google, Microsoft, Opera, and many others.
Gecko which powers Firefox - Supports most web standards and is worked on by Mozilla who are lagging a bit and had to fire a number of their employees recently (unfortunately).
Webkit which powers Safari - Supports the least web standards and is worked on by Apple when they feel like it.
In summary: Safari is the worst browser in terms of implementation of web standards, and for use for web applications by a long shot, it's become the new Internet Explorer.
Regards,
A web developer of 20+ years who's contributed to the web standards bodies he's currently moaning at Apple for not complying with in this post.
PS: I thought I'd just throw in this edit to point out I'm not either for or against opening the app store up for side loading, I would just like Apple to stop violating web standards, and quit pretending like their browser is anything but dragging it's feet - especially on iOS where you can change the default but NOT the rendering engine behind the eye candy.