Well, if we lived in some parallel universe, where Yamaha were the ONLY arranger maker, I'm sure some of this might make a lick of sense. But we don't
Neither Korg, nor Roland seem to have ANY problem whatsoever with arrangers with 76 keys competing against their WS's. Maybe because they assume that a sale for Roland or Korg is a sale for Roland or Korg, no matter WHAT type of keyboard it is...
And the Korg is the ONLY arranger that it's basic feature set (editing, sampling, voice creation, etc.) is almost identical to it's WS line (at least the older Tritons). Neither Yamaha, nor Roland have ANYTHING from their WS line in the OS. Some samples, and the underlying main synth chip (but with ALL the WS features disabled) is all that they have in common. The rest is entirely arranger based.
And that old chestnut of the WS boys complaining that the T2's SA voices sound better... Well, that's the EXACT proof that the 'divisional rivalry' theory is bunkum. If there WERE any divisional rivalry, the MotifXS line would have NEVER gotten the SA technology in the first place. After all, the arranger division invented it and implemented it first!
Might as well blame the Freemasons! Those damn Rosicrucians are always messing things up for the 'pro' arranger player