First thoughts from Entrenchment gaming:
The starbase upgrade paths for the TEC are drastically out of whack in power. The bonus armor/hull upgrade adds as much HP as the original starbase itself - you get a starbase with an extra starbase strapped to it, essentially. Then you get two more with the third and fourth upgrades.
On the other hand, the modules for trading, ship construction, and strike craft squads are really weak, since if you wanted those things you could just build them normally. Trade ports, frigate yards, and hangar defenses are both cheaper and better than the starbase versions and don't take up starbase upgrade space. Sure, the starbase version lets you build frigates from an uncolonizable gravity well, but that isn't actually a very useful ability, especially since you have to research it and add 2 modules to get the full build rate. On the other hand, building ships from a nearby shipyard and setting the rally point to an uncolonizable gravity well is free.
The "extreme long range" missiles added by the second weapon systems upgrade don't have long range at all, never mind "extreme" long range.
The TEC starbase absolutely does not fulfill the role of restricting enemy movement or defending a planet by itself; you can easily go around it. The AI in my game achieved this entirely by accident. I had a starbase at 5 o'clock in a gravity well with a 5 o'clock phase lane to an enemy planet. An annoyance fleet of enemy purge vessels jumped in from that phase lane but arrived at 3 o'clock - they had jumped from the north end of the source system, so arrived somewhat north of the phase lane in my system. They waltzed right around the starbase and started bombarding my planet. They had also evaded 2 fields of mines at 5 o'clock. Other AI ships did the same thing by jumping to 7 o'clock or 3 o'clock positions. The starbase was totally ineffective at defense.
However, you can easily use starbases to conquer enemy worlds, since they build very rapidly and the AI isn't smart enough to ignore them if they're out of range. I sent a scout and a starbase constructor to a pirate system. The scout played decoy while the starbase built; then I queued up all the hull/shield and weapons upgrades. The starbase destroyed all the in-system pirates on its own. You can do the same to AI players by building a starbase in their system; the starbase builds HP up faster than they can shoot it down, even very late in the game.
On the other hand, the AI tries this tactic sometimes but is very bad at it. A Vasari AI built a starbase in one of my systems and sent it to attack a Gauss cannon. But a nearby repair bay healed my cannon faster than the enemy starbase could damage it. With the help of some strike craft from an in-system hangar bay, the starbase was killed with no losses. I didn't even notice that my planet was under attack until the enemy starbase was already 50% dead, and my cannon was still at 100% health.
Likewise an Advent AI tried to retake a world I had just conquered from them by spiking it with a starbase, but built the base in a location where it was completely out of range. It launched two bomber squadrons to attack. I countered by queueing up two hangar defenses with 2 fighter and 2 bomber squadrons; the friendly strike craft destroyed the starbase, again with no losses of any kind. In total, the starbase was as threatening as an immobile Percheron, but cost my enemy about 5 times as much in resources.
Starbases don't have flak weapons, so they're completely defenseless against carriers or hangar defenses. Even if the starbase builds strikecraft, you just need enough fighter squads to suppress their strike craft, plus a few bombers to deal damage, and you can pinprick the base to death. Vasari starbases can chase the carriers around but aren't fast enough to catch them.
