50 hp is stupid, one thing I've learned from balance is you change aspects of a unit / object one attribute at a time and see how it affects the meta. And you change it by a little, I think the speed change is satisfactory for now
This is one of those times where I think the devs have it wrong. They did say "all units would be relevant at all times of the game". And that's cool. But historically "direct upgrades" have proved that the older unit is teched out, and there are games that do the "basic units are still viable at later tech levels" by making those basic units not completely out of date when later tech levels are achieved, simply by making those later tech levels provide more interesting roles. I don't really think that planetary annihilation has enough depth in its tech tree/combat systems to make strict upgrades viable.
Gil-Es are fine. Lets just make the game so no units can kill anything and people can turtle all day and make nukes.