@Marty To add on to what Hifi says, I think there is most definitely a marketing aspect as well as some revision of history.
It’s been widely repeated that the original Pro X was intended to be the “Next Generation Surface” but also crucially was intended to be Intel based and that the SQ was in essence a fallback option since Intel couldn’t deliver suitable chips.
So fast forward to today I think the reason (and borne out by the way MS was talking at the event.) the SQ3 system wasn’t a Pro X2 or some similar name is that MS is essentially saying that ARM is mainstream Windows now and is just a configuration option that has some unique benefits including 5G, the neural stuff and better battery life too.