You're leaving out Casio. In 2016 (AFTER the E-A7), Casio released the MZ-X500 which was their most fully-featured arranger/synth since the MZ-2000 in Y2K. It had a large screen, multipads, stored chord progressions, etc. For a few reasons, especially the crappy keybed, it didn't meet with widespread acceptance but the potential is/was there. Like Yamaha, Casio sells a LOT of keyboards at the entry level. Most, or at least many of them have arranger-like features which will create expectations in their user base. They have the software and feature set. Arrangers are 80% software so the hard part is done. The remaining 20% is CONTENT. There are plenty of 3rd-party utilities that will convert older Yamaha styles. Unlike Rolands, Casios are "smart" enough to read and render the styles faithfully unless they use MegaVoices, etc.

If Casio releases a "CT-S900" with on-board style creation, perhaps a few more physical buttons and a larger display, it would be knocking on the door of a Roland BK-5, at least. Casio are a MUCH bigger player in terms of numbers than Wersi, Bohm, and Ringway, all of which I've only seen a handful of times in the USA. More portable and affordable, too.

Ketron? They are a pimple barely worth mentioning. How many boards do they sell worldwide? Also, they have a habit of releasing the next model before all of the bugs are worked out of the previous one. Support? Exactly ONE provider in the US, and perhaps none in Canada. If you watch some recent YouTube reviews by a dedicated and open-minded expert, caveat emptor (and this echoes my own personal experience with this brand.)

IMO there is room for another volume player. Software, source code can be sold. I've said it before, if Roland doesn't want to build a dedicated arranger (and it seems like they don't), then they should embed some of their arranger source code in their MIDI controllers, combo organs, or license it to another company. My $.02.