I never talked about people who switch from Android to iPhone, or questioned the value of that application. You did.
I questioned your claim, which is that "people wanted bigger phones and went to Android to get them only to come back when Apple also offered them". If your claim were true, Apple would have gained market share at the expense of Android since the release of the iPhone 6 and 6+. It didn't happen. More people chose Android over Apple than ever, despite the larger iPhones.
No, this is where the marketshare numbers fall down.
It is possible for Apple's marketshare to fall while still gaining switchers from Android *and* for Android's marketshare to rise because it's not a zero sum system. The total numbers of smartphones are still rising, with android taking the lion's share of them since they have the whole market segment to aim at and not just the premium end.
People switching back to iPhone will not necessarily increase Apple's share relative to Android if even more people buy an Android phone who didn't have a smartphone before - the figures for total phones sold year on year bear this out.
And yes, your exact quote was "Yeah, of course we should blindly trust these numbers." - numbers that specifically tell Apple (collected by themselves and other polling services) about what *they* should do.
The question purely becomes "do you trust that Apple's choice to release a migration app is a genuine use of funds and effort, or is it part of some grand conspiracy designed to make it look like people are buying iPhones" ?