I don't think you realize what you'd lose without third party apps:
No Netflix, no Facebook, no Banking Apps, very few (if any) Games, no VPNs, no private mail clients, no 3rd party calendars, no third party podcast apps, no dropbox, no kindle, no authenticators, no bluetooth utilities to control your smart home device, no ticketing apps, no ride sharing apps, no weather apps, no game emulators, etc...
I could go on and on. The third party app ecosystem is not so small that Apple could have just bought them all during the iPhone's rise. The amount of money poured into iOS app development by third party devs is not trivial and it absolutely has made the platform better.