Pianoteq runs fine on my original iPad Air (first gen).
As for the sampled-vs-modeled debate, though I can understand the merits of some sampled ones (and I have dozens) on a Mac, this is different on iOS, as there are not many, if any, large sampled grands except for Ravenscroft. And that one’s surely flawed compared to the Mac version.
Pianoteq easily rules supreme as long as there are no 50GB pianos on iOS. And even then. No sampled piano lives up to Pianoteq’s playability and real piano feel, even on a Mac.