These are not really rivals - they are two different rungs. The R21 Ultra puts out 21 Nm from Moza's newer flagship motor architecture and scores near the top of our rubric; the Alpha EVO Sport 9 is a 9 Nm entry base that exists to get people onto Simagic's 21-bit encoder cheaply. Line them up and the Ultra wins nearly every axis, which it should, because it costs $300 more and plays in a higher class entirely.
So the sensible way to read this is by budget and ambition. If you have around £600 and you want a base you will not out-drive for years, the R21 Ultra is the buy - it turned Moza's R-range from good-for-the-price into a proper flagship, and 21 Nm is torque you grow into rather than out of. If £399 is the number and you are taking a first real step into direct drive, the Sport 9 is a perfectly good place to start, and it leaves the Simagic ladder open above you.
What I would not do is agonise over the rubric gap between them, because it is mostly the tier talking. The question is not which is better - the Ultra is, comfortably - it is whether you are spending flagship-lite money or entry money. Answer that first and the pick makes itself.