Well thats what i thought, but looking back through TRO3085 its close to a 50/50 split and TRO:Prototypes none of the DCMS mechs use it.
Considering their 'Mechs from Prototypes consist of a basic Gauss carrier using an unpopular chassis and an underwater combat specialty unit, I don't really see that as indicative of what the DCMS is using in the 3090s.
As for 3085, let's take a look -
LCT-5W2 Locust - Everyone is described as fielding it. It has C³ slave
MON-86 Mongoose - Doesn't have C³
HM-1r Hitman - A variant already exists with C³ slave. Refit is of existing version that did not have C³ slave.
NX-80C Nyx - New C³ slave variant
SDR-7Kr/8K Spider - A variant already exists with C³ slave (7KC) which is concurrent.
JR7-C4 Jenner - Possesses
boosted C³slave!
PNT-13K Panther - A variant already exists with C³ slave.
PXH-7K/8CS Phoenix Hawk - both carry C³ slave
GST-10 Ghost - Import, no C³
SKW-2F Shockwave - Import, no C³
TSN-1Cr Tessen - has C³ slave
GRF-4R Griffin - common refit throughout the Inner Sphere, no C³
SHD-3K Shadow Hawk - has C³ slave
TFT-C3 Thunder Fox - Combine variant has C³ slave.
DRG-5Nr Dragon - C³ slave
DRG-7KC Grand Dragon - possesses
boosted C³ slave!
OSR-4K Ostroc - no C³
ARC-9M Archer - produced by multiple nations, no C³
DAI-01r Daikyu - possesses
boosted C³ slave!
NDA-2KC No-dachi - possesses C³ slave
MAD-9W2 Marauder - possesses C³ slave
CGR-3Kr Charger - refit of chassis that originally lacked C³ slave.
HTM-28Tr Hatamoto-Chi - possesses C³ slave
VTR-Cr Victor - possesses
boosted C³ slave!
BLR-K4 BattleMaster - no C³, but multiple previous versions possess C³ Masters
GUN-2ERDr Gunslinger - C³ master
AKU-2XC Akuma - possesses
boosted C³ slave!
CP-11-C3 Cyclops - possesses
boosted C³ master!
OR-2I Orochi - no C³
NG-C3Ar Naginata - possesses
boosted C³ master!
PKP-1A/1B Peacekeeper - possesses C³ slave
So, as you can see, the vast majority of the 'Mech designs the Combine gained in TRO: 3085 had C³ or boosted C³. In instances where they did not, it was generally because it was a foreign design a refit of a chassis that previously didn't have C³ to begin with, or a 'Mech that already has serviceable C³ equipped variants. The only exceptions to those specifications are the Orochi, Mongoose, and the Ostroc.
Considering that a large number of new C³ equipped variants were added to the DCMS by TRO: 3085, and in fact the faction has continued to push development of the technology forward by creating units using boosted C³, I'd have to say that evidenec actually points towards the DCMS continuing to favor the technology.