Also this has always bothered me before switching whenever I used a friend's iPhone for a moment.
The trouble alread begins when some link in Safari opens a 3rd party app.
Sounds weird, but Apple could really learn a lot about UX from Google regarding this "go back" interaction.
It really was a joy how reliable it works even for inception-level nested app interactions.
On iPhone, half of app switches (at least) require me to swipe up or go to the home screen.
And positioning the unreliable sometimes-available back button at the top left has made me drop my phone at least once.
For all that's to like about iOS, "navigation patterns" are not one of them for me.