I unlock Mil IIIs early in every game as well. The full decloak, knockback, improved durability, all on top of +100% damage? Perfect for my playstyle, which consists of turrets where required, and lots of fleetships.
And that's part of the problem with the old Mk V turrets. When they were per planet, but other turrets were per-galaxy, capturing/hacking the Mk Vs become essential. Every game started with "Explore to find the Mk V Turret Fabs, then capture/hack at least 3 of the good ones, THEN proceed with the rest of the game." I almost never used normal turrets anymore, except for Fallen Spire games. Instead, I could focus on fleetships, like I prefer to do.
But without anything being per-planet, we're reduced to the "Chokepoint uber alles" scenario, where the only way to have enough defenses to fight off a large exo or CPA is a chokepoint. Which means you can't protect stuff like Fac IVs or Fabs, and there are all the usual complaints about how worthless they are because they die in minutes.
I switched from supporting chokepoints to per-planet caps because it meant that
a) normal turrets were useful again
b) all map types were equally viable (I like Honeycomb, but could never play it under the old Chokepoint regime)
c) Beachheading was useful for more than temp niche cases
d) Forts and per-galaxy Mk V turrets could still make chokepoints to deal with Exos and Showdowns and their ilk
aka, I found the game more fun.
I find that energy costs are close to balancing out the defensive power of turrets. In many of my games, 50% of my final economy goes to Matter Converters to support my fixed defenses, especially in my 10/10 games. That's no minor matter, and a serious drawback should I ever fleetwipe, or even just lose a few worlds to an Exo or CPA.
(In fact, I'd love to be able to unlock an improved efficiency Matter Converter Mk II...)