Really tiny Torx screws are easy to strip the head on. I've done it more than once, to my considerable regret.
Pentalobes are harder to strip, because a pentagon is less like a circle than a hexagon is.
Are they the Platonic ideal of a screw head for the exact size used in iPhones? No idea, I'm not a mechanical engineer. Just a klutz who has stripped a few tiny Torx screws with my big ol' meat hands.
Isn't Torx basically a hexagram rather than a hexagon? To me, pentalobe looks closer to circular than Torx does. Also, how much have you worked with tiny pentalobe screws compared to tiny Torx screws? Is it possible you've seen the latter strip more just because you've used them more?
Can you name a single advantage of pentalobe screws over pre-existing standard screw heads like Torx? If not, then Occam's razor is how I know.