As a web developer who suffered through IE6's pain-points from its heyday until 2014, I've said this about Safari on iOS for years now.

I had a huge retail client who's customer base was largely on Win 2000/XP equipment, so they insisted on it until usage dropped off enough. Sorry I can't be more specific.

Luckily, it's not actually quite that bad yet, but I've built PWAs and some of the bugs are truly awful.

I think it was iOS 11 where the camera didn't even work in PWAs for months- we had to get people to use the website through the actual Safari browser on their phone. It wasn't actually fixed until 11.3. It was brutal.