the idea of "getting more done with less, thus Omni, being valuable in the DA era" also makes sense. one of the strangest ideas of MWDA to me was that in an era of reduced military size omnimechs would be less common
Consider it from a different angle though; Not only were militaries smaller, but a LOT of what was left of the infrastructure was either not being rebuilt, or was not being rebuilt by people with the slightest clue what they could use, support, or need.
witness the LC concentrating ALL of their shipbuilding in one system and giving it jack shit for protection, in an
interstellar nation. This would be like only having one port capable of repairs for a nation made up of hundreds of islands-it's a big port, but it would have to be MUCH BIGGER to handle ordinary civil demand, never mind the demands of actually having a navy at all.
add in Nations NOT having a reliable backup to an infrastructure item without which they can't really remain nations (wholly dependent on HPG networks you don't control? really?? even for your classified commo??)
so people saying "why yes, I adore the idea that I can't maximize the use of ever cubic meter and kilogram of cargo for my logistics because I'm fielding 36 different designs in a battalion of 32 'mechs or tanks! let's do that!!" is right in keeping with the rest of Stone's 'Reforms' and the illogic of it, simply dovetails into the illogic already infecting the setting.
I mean, your smaller militaries were also getting heavily into logistics-heavy ICE engines even on battlemechs, while also reducing their logistics and complicating it by running non-omni designs and lots of variable specialists that don't have any parts in common.
This path leads to madness if you actually bother to contemplate it, so the best advice is to nod your head, accept that during Stone's Peace everyone in the command chain was a braindead moron, and move on.