Threads like this serve no productive purpose.
If my understanding is correct, you are saying that
1. you only want to run 'Mechs in the game,
2. you are not coordinating at any level with the other members of your team, and
3. you are getting wrecked by unopposed airpower from the other team.
This doesn't seem unbalanced at all, and is the outcome that I would expect given your scenario.
'Mechs are
not going to be effective against aerospace and VTOLs with the exception of some lucky shots here and there and opportunities presented by pilot error. That is why both teams have access to both aerospace units and AA tanks. If you personally don't want to play in either an aerospace or an AA tank, then for the good of the team (since everything is team based in MWLL) your team will need to field some AA or counter-aero units. If you don't, it doesn't matter how many MKII's and Awesomes you deploy, the guys up in the air will have their way with you... which is pretty much what you are saying is happening.
Sounds like the mod is working just fine!

And yes, you are playing MechWarrior: Living Legends, a combined arms game that includes more than just 'Mechs. The mod is, of course, in its first beta release, so there are features that have not been introduced and some bugs and quirks, please be patient while we address those.