Don’t assume Yamaha are not getting this right. The things that are important to you Yamaha may not consider hugely marketable.
Arrangers, even the TOTL models, are largely bought by people who want to sound good playing basic stuff, and things like 13/8 time signatures, multiple time signatures, vast memory space, etc etc mean little to the average arranger customer.
I think Yamaha knows that if they want to sell significantly more arrangers the keys are — make it sound even better, make it lower cost, make it even simpler to operate. Adding features that suit only very advanced users may not be their corporate direction. Products like the DGX670 seem to me more like Yamahas chosen direction rather than making TOTL arrangers more acceptable to advanced users.
Mike