Well zK is based on AA/BA (or if you want, Total Annhilation) so that is where the many units come from.
The way zK is designed now you can not simply remove units:
1) Each factory is supposed to be viable at start and in almost every situation.
Since factory design is an extension of the
So with 11 factories you need 11 raiders, 11 constructors, 11 anti-air, basically every unit role 11 times.
Even if you reduce the factories to "ships, tanks, cloaky, airplanes" you still have that redundance.
2) It is supposed to be playable 1v1 and with big teams.
For that needs some superfusions, big striders and so on.
Compared to (1) that is only a handful units but might explain why inherited lol-units like Buzzsaw/Rave Party were kept.
The idea of taking some spring game and making a "simple version" from it came up for every TA-style mod generation.
Afaik it never was done, maybe because people realized it would just be a watered down version of the original?
Still I think spring "needs" a more simple RTS.
But basing it on zK (or other game) would mean it gets seen just as some funny experiment.
It would need to be a completly new game.
There was some, like Nanoblobs or Kernel Panic but those are far from tradionel RTS so not comperable.
Atm I can only think of two spring games that did/do not have this explosions of unit numbers:
-P.U.R.E.
-The Cursed