That is a great point Halvagor. You do hear about the ComGuards utilizing combined arms in a more extensive way than any other InnerSphere military. However I have never seen anything about mixed Level IIs or Level IIIs. It might be interesting to have a Level II of 4 Mechs and 2 Fighters (a half company of raiders ideally deployed in a Leopard class Dropship) or a Level III of 12 Mechs, 12 Vehicles, and 12 Infantry (2 Level IIs each). Be interesting but instead you get the monolithic Battalions that make up a Combined Arms Division.
The combined-arms integration within Level IIs may not be explicitly stated, but is directly implied by the composition chart on page 9 of FASA 1714: Field Manual: ComStar. Only 6 of the 24 types of formation (Delta, Epsilon, Zeta, Rho, Sigma, Tau) have BattleMech forces divisible evenly by 6. Therefore, in 18/24 styles of division there is at least one Level II which is of mixed unit types. Most will have at least two Level IIs of mixed models. And, as MadCapellan pointed out, a lot of published scenarios assume a mixed-unit Level II.
Still working up my revised ComGuard compositions which you will see in Clarion Call. I wanted to ask your opinion on a new formation I call the Apex. Composed of 5 BattleMech Battalions (180), 1 Aerospace Fighter Wing (30), and 1 Infantry Half Company (6 platoons) it is the ultimate ComStar assault force. This isn't very combined arms I grant you but such a force would pack the greatest battlefield punch. Efficiently deployed by 5 Overlord Dropships which plays well if operating in Battalion sized taskforces or one giant sledgehammer. While the Mech force is the primary strike force of this powerful formation it is ably supported by fighters who are tasked with ground support. The Infantry force while the smallest would likely be special or elite forces (Battlearmor) who could be used to perform select operations in support of their Mech brethren. Vehicles are dropped completely from this premier front line force.
I think the value of massed battlemechs is overstated. While it's rare for a lance of armor to overcome a lance of battlemechs in a straight-up fight, my experience with regiment-on-regiment MegaMek battles indicates that two battalions of medium-heavy 'mechs with two battalions of medium armor can defeat three battalions of heavy-assault 'mechs without too much of a stretch.
Early sourcebooks bore this out, as well, especially in the writeups of the Fourth War, where it was often said that it was the FedSuns' RCT combined-arms teams which allowed them to win fights, not just their better strategic planning. As late as the publication of
Bush Wars the Defenders of Andurien's combined-arms loadout (which was never specified) is listed as one of the reasons for their success in Andurien's bid for independence (and lack of it is cited as one of several reasons the Canopians performed so poorly).
But through most of the Clan War all anyone talked about was 'mechs, 'mechs, 'mechs -- during the Blood of Kerensky series only twice do vehicles play any significant role in battles described, at Wolcott (where the Kuritans curb-stomped the Clanners good) and with the ComGuard -- but on Tukayyid the heavy armor Level II butchered by Phelan's light recon star was 1) stupid 2) all heavy vehicles and 3) not supported at all by anything else. I tend to think that a single standard FedCom RCT should, by itself, eat your average Clan Galaxy for breakfast -- especially if bidding is involved on the Clanner side. Because 3 regiments of armor should have a say in the fight, rather than being ignored completely as happened in just about every description of a Clan engagement with an RCT.
I think your Apex formation would still lose in a fight against a decent FedCom RCT, which makes up for only having 66% of your 'mechs by fielding 324+ armored vehicles, and a battalion of artillery (forget the Poor Bloody Infantry, though I suspect the RCT could defeat your Apex without its 'mechs at all); you're even on fighters.
But the Apex could probably give a Clan galaxy a straight-up fight.
My revised Alpha formation adds 4 Mechs (168 BattleMechs) and 2 Vehicles (6 Vehicles) while dropping 3 Infantry (6 platoons) and 3 Fighters (36 Fighters). This rounds out the Battalions of this unit nicely giving you Level IIs of Vehicles and Infantry. A Level III of Aerospace Fighters with 4 Battalions and 1 Company of BattleMechs. However I could shrink the Mech complement further by taking that company of Mechs and splitting it into Vehicles and Infantry. That would be 4 Mech Battalions (144), 1 Vehicle Company (12 Vehicles), 1 Infantry Company (12 Platoons), and 1 Fighter Battalion (36). What do you think?
My honest assessment is that you'd be better off with 4 vehicles & 8 infantry, provided one of the vehicles is a Mobile HQ. If not, then I'd just do 12 Infantry, because then at least there's someone to guard the techs at all times and the 'mechs at night when the pilots are sleeping. 6 vehicles, unless one is a specialized command unit like a Mobile HQ, aren't going to add anything to the fight; 12 infantry can at least guard the supplies from thieves.