I share your complaints about 3rd party keyboards in iOS, but just a heads up in case you hadn't noticed: Google's Gboard recently added support for Dvorak and

I share your complaints about 3rd party keyboards in iOS, but just a heads up in case you hadn't noticed: Google's Gboard recently added support for Dvorak and Colemak, and is by far the most stable/usable 3rd party keyboard I've used.