Yeah, that has been always a thing since i have memory. Problem is that i came into problems trying to integrate BAs into my force without omnis to carry. They either go hopping around, or i have to get them a carrier.
There's a reason I made sure to give the Empire the ability to build BA with magclamps. :)
I would have no problem with OmniMechs in Omega Galaxy. Once they have sufficient OmniMech production capacity, non-Omnis would be replaced everywhere, save where pilots choose otherwise. Seeker Galaxy, for example, is where one would expect old SL 'Mechs. Eta might favor any non-Omnis built on former Hansa worlds. Omega's non-Omnis would be sent to PGCs and solahma units.
The intent, of course, would be to equip their entire touman with the best equipment they can build. Their resources are not limited as they might have been in the Homeworlds. They should have a production excess (this is shown in Spotlight On: Hellion Keshik, in that the MechWarriors each have two 'Mechs), so after filling out their own ranks, they can export the rest via the vast Hansa merchant fleet. The exported equipment, one might guess, would not be their top-of-the-line products. No need to give potential foes your best stuff.
One thing on Sarna that I take issue with is that Grunt Galaxy is listed as part of the
touman. Grunt Galaxy was formed during the Crusade out of desperation, due to casualties exceeding projections. It would not have remained a Galaxy after the Crusade. Those troops would have reverted to their PGCs (or law enforcement, whatever) after the Crusade. (At least I don't believe it's stated anywhere that it became a permanent Galaxy...)