Arturia seem to have abandoned the development of iPad versions of their synths despite the fact modern iPads and especially iPad Pros are easily powerful enough to run them, and despite mobile computing being indisputably the new bandwagon that forward-thinking developers are jumping on.
The (few) iPad Synths that are available desperately need a refresh and upgrade: only the iSEM can be used as an audio unit, while the iSpark, iProphet and iMini are bordering on being obsolete, because they support only the deprecated inter-app audio protocol which app developers and Apple are abandoning.
Other manufacturers are leaving you behind creating really powerful iPad synthesizers, some of which are even free. I won't list any here because that would look like an advert for competitors' products, but presumably you are astute enough to see what's going on in the market. What gives?