The Sound Variation API comes up short for a number of reasons.
The point you make is, I think, related to the fact that different dimensions are quite often best handled by a multi-group articulation manager such as provided only by Cubase expression maps.
having every possible combination of keyswitches listed as seperate articulations is indeed very unwieldy in many cases.
For the case of Synchron, the total number of "rows" in the articulation lane should be DIM1 + DIM2 + DIM3..etc.. rather then DIM1 x DIM2 x DIM3, etc... Even the Synchron Player itself presents things in this kind of fashion...but unfortunately StudioOne, LogicPro and DP do not have have multi-group functionality in their articulation managers as of now so the only way they can handle all the possibilities of multiple dimensions is DIM1xDIM2xDIM3, etc..resulting in combinational explosion. Only Cubase expression maps can handle up to 4 dimensions that way.
I have been able to code around this limitation in LogicPro using scripter and automation lanes to provide the other groups.. But I am switching to DP now...so...won't be any help much longer.
At least in the case of DP, one good news is that DP saves the results received via Sound Variation, into a json file, which you can edit after that if you like...and then basically just ignore Sound Variation after that. So maybe you can write a script that can manipulate the json as you wish to reduce all the dimension multiplication...
Cubase groups still have combinatorial problems (consider using a group for per-note accents, it's still a multiplier). What matters most is the idea of directions, which, like directions of notation, are not specified per note and stick until superseded by another in the same category. It's only when a group is specified as a direction that the combinations decrease.
Getting VIs and DAWs to agree on a system for directions too, when so many don't have any representation of the concept, seems like a dream never to be realized. However, if VIs could let you control what gets expressed as sound variations (articulations), you could limit that to proper per-note articulations. The number of other directions (controlled via e.g. CCs or automation) is usually small - bowing style, vibrato, muting etc, and most DAWs have reasonable ways to set and chase CCs.