The thinking behind uses of the starbase are as follows:
Vasari bases are for area defense and economic boostage and importantly can be used as offensive weapons - jumping in an escort fleet to guard the starbase as it is constructed at the edge of the well, then leisurely strolling along and crushing everything in its path (and with frontal shields, that includes other starbases).
TEC Argonevs are for point defense and establishing forward bases. They can't move so their use in offense is approximately zero (not necessarily a bad thing as they have other strategic uses).
Advent Transcencias are for (slightly larger) point defense and culture; they're a bit better at dominating no-man's-land areas like suns and roids than Argonevs but dont have as much straight-up military or industrial application.
On paper these dynamics work great, but in practice they have an unintended side effect: because Vasari bases can move to respond to a threat from any direction, they are much more effective for defense and destroying enemy fleets. TEC and Advent are forced to build their bases in as annoying a spot as possible, then buy offplanet government upgrades and spread other defenses all over. The enemy fleet jumps in, toasts everything but the base, then attacks the base on its own sweet time.
In other words, the mobility of the Vasari base means the Vasari bases are massively superior to their analogs. This can be balanced by
a) Giving the stationary bases massively extended range (not a good option because range any further than it currently is would make the base devastatingly OP).
Giving the bases engines. They should not be as fast as the Vasari base - in fact moving less than half that speed would still serve the purpose. This simply gives the player the flexibility to move the base to the place it can be most strategically effective while still being forced to think because it takes awhile to drag the base over there.
The designers are reasonably concerned that giving Argonevs and Transcencias mobility would give them the capacity to function as offensive weapons. But considering the ponderously slow speed of those bases, their application in an enemy well would be very limited. If this is still a concern, it shouldn't be difficult to add a stipulation that Argonevs and Transcencias cannot be built in grav wells controlled by enemies.
Players should be able to build a starbase, upgrade it up the wazoo, and have a solid confidence that the well it occupies is safe from any but very concerted attacks. Vasari players can do this. TEC and Advent players can't. Giving those players very slow engines would fix this.
PS. Love the Beta 2 changes ... weapon banks and mine balances make me happy. : )