You're comparing wrong models though? X9 and X300 Pro are both much larger than the phones I mentioned.
(I've just noticed you also used wrong models in your original comparison - while both phones are larger than the mini, the difference isn't as large as your link suggests)
The iPhone is normal phone size width and depth, but it's meaningfully shorter than just about everything else. It doesn't sound like much on paper but I've always found it adds up once in a pocket. (All dimensions height x width x depth, in mm, rounded up to the nearest mm)
In fact, they're more like the size of the full size iPhone, which, if you're sticking with your iPhone Mini because the iPhone is annoyingly large, means they're too large.
(For reference, I would really like something a little bit smaller than the Mini, but there’s nothing remotely modern that exists.)