I am honestly not sure if increasing the DD cap will help a lot early-mid game. With frigates, I notice Vagyr tends to make a second CC, push them forward and spam produce-HMFs so fast that if you can maintain unit cap even against significant opposition.
Basically, 21 HMFs engage 6 DDs, but every time a HMF or DD dies another one starts building just outside of missile range. By the time you lose your first 21 HMFs you likely have at least 6 more (3 production rounds) having entered the fight, so say that evens it so there are only 2 DDs left facing the 6 HMFs. You then have 2 DDs + production vs 6-8 HMFs + production (9-12 if you have a 3rd CC or the flagship moved up). I am not sure if 2 DDs can kill the HMFs faster than they are built, if that many are left at all.
I am not 100% sure, but I think FFs get a bit too big of an edge from being CC buildable (you can never make more than 2 DDs in parallel, and you need a SY for that which will never be as close to the front line as a CC or MS can get), so you essentially end up replacing losses during the battle and running over the DDs which can’t be replaced as easily.
There is also the fact that you often start the fight before more than 2 DDs are built, and you can get 21 HMFs way faster than 5-6 DDs and likely even faster than one BC for Hig.
Hig is a bit screwed frigate vs frigate, since torps can’t compete with HMFs and Ions require the advanced research module, adding enough of a delay for Vagyr to reach spam-levels of ships.
The only techniques I have seen work for Hig is swarm (with support from another player), torpspam (supporting a swarm or HMF spam) and Ion Spam (which is basically a slightly slower HMF spam.)