I'm mostly a Mekwars server player, so my experience might be biased, but after around 70-80 games in FWL, I found that a BV-balanced army of FWL machines generally work just fine.
Loving it. That's good stuff, the force you described.
What I'm about to say is mostly for someone else's benefit, since you obviously 'get it' and are doing great... just using your words to bring up the topic: Your results aren't a surprise. If you're playing on anything larger than a single map sheet, FWL forces have room to fan out and take advantage of their above-average speed. Then we do just fine.
The 'problem', and I say that in semi-quotes, is FWL requires a lot of precision in play and army design. We're genuinely harder to play than most factions. The developers have been reluctant to give us "3/5/0 movement, tons of armor, stack in as many gauss rifles as possible" turrets for one of two reasons.
1 - Back in the FASA era, I'm convinced the developers either didn't care about us, or may have viewed us with some kind of passive disdain. Probably just "did not care." I'm sure you know just as well as I the kind of worthless garbage they gave us. GRF-5M, etc.
2 - In today's BattleTech, the developers seem to have wisely understood that you can't make every faction into 'Conventional Davion-Steiner style straightforward optimized gauss platforms.' Hell, even Davion and Steiner aren't getting as much of that these days. We pretty much never will get those because making every faction fight like that makes the game boring as hell. Even our 'dual gauss' units have some quirk; the MR-5M Cerberus gives up the second Gauss in order to be more durable. The Carronade uses mixed types of Gauss but otherwise fits the 'optimized design' paradigm very well. Giving us Thunder Hawk clones would be a bad idea.
It would be like if Street Fighter only had Ken available to pick. Sure, the majority use Ken just like the majority used FedCom back in the day. The game would lose its appeal fast if not for the folks who pick the other characters to provide contrast, though. Same deal here.
We sucked, past tense, in the FASA era and early CGL era. They seem to have gotten the message after the WLF-3M that we were sick of being the trash faction, and they found people who could design viable machines that use a whole different combat style. Today we win through a mix of special munitions and excellent medium-range superiority machines such as the TDR-10M. 3 or 4 TRO books later, we're no longer garbage-tier. We're viable, we can win, and we're fun.
Incidentally, reading up on what you've been doing to win has been fun too. Glad to see your army design is working well!
EDIT: A question about Branths. I hear they can only be used on certain worlds? Is that right? A shame if so, because if 'infantry spotter on a hill' is fun, a FLYING infantry spotter ought to be even better.