I think it's fair to say that early on, third party developers added a lot of functionality that was lacking in the OS. Apple has steadily incorporated the more popular features so that is probably less true today, but there are still lots of bespoke tools that they are never going to provide. To use a personal example -- if only Android had a Tesla app, it would definitely be a factor in my choice for my next phone. If they ended the ecosystem altogether I'd probably switch. Whether that also applies to regular people is of course debatable.
There's a huge difference between indie developer apps and corporate apps.
I need my bank's app (well, all four of my banks' apps actually), my email provider's app, a few games, etc. I might have a couple of "indie" apps, maybe. But I could certainly live without them.
