If cross-platform tools are always behind because the native platforms change more quickly--and I think you're correct about that--then so are native apps that

If cross-platform tools are always behind because the native platforms change more quickly--and I think you're correct about that--then so are native apps that aren't constantly rewritten for the latest OS version. And then so are the native apps running on not-newly-upgraded client devices. And since these quickly changing native OSes change in different ways, remaining "fully native" requires your app to have different UIs and feature sets, not just on different OSes but on different versions of those OSes. If you have the resources to keep upgrading separate native apps for all the latest combinations of hardware and OS while also maintaining older versions, with different UIs and feature sets for each, you can have all the benefits of "native". Anything less, and you are deciding to live with less than "full native" and have to decide which compromises to make. In that case, you might go for maximum speed with a consistent--therefore non-native--UI (PhotoShop), or good-enough speed with non-native UI that runs consistently and on even more platforms (a web app), or give up all but one OS but support all OS versions on all hardware (some dental office Windows app that hasn't changed for 15 years), or whatever. Or some cross-platform toolkit that will never completely keep up with "native" but might be okay, because you can't keep up with native either.