The allergies people have to mobile bases is fairly odd.
1- If you're going to build a large, expensive, militarily useful platform... figuring out how to make it *move* is an obvious step. We build aircraft carriers as mobile airbases; we build armored vehicles instead of gun emplacements, unless the gun is so huge that anchoring it to the planet improves accuracy. Mobility is central to warfare.
Unless there's a physical or logistical reason why it can't move, or why that movement would be useless, the logical thing would be to figure out how to make it move. Is anybody seriously arguing that it would take more resources to move a base than a maxed-out fleet? Or that they'd rather be an obvious target for long-range toys like the TEC's superweapon, firing a projectile suitably modified with a proximity fuse? I don't see anybody suggesting that the bases should be anchored to the planet to absorb recoil from a massive projectile weapon, or to use an ocean as a heat sink for massive sustained fire, or that they're so small that an engine wouldn't fit. Is the argument that engines are non-scalable so that it's impossible to provide sufficient acceleration for them to ever reach escape velocity?
2- Is it 'an abuse' if somebody moves his fleet into your space, when you're permitted to do the same thing? If anything, moving a base into your territory should make it easier to kill.
See Netrek for a classic game with mobile bases. Incoming base? That's not abuse; it's a target. Sure, it's fairly powerful, particularly in the hands of somebody well-practiced. But there are techniques for killing them, and if your team is playing so badly that a single very slow-moving ship is causing you trouble in your own backyard, your team probably deserves to lose... and in Netrek, your team didn't even have to invest a large quantity of resources to construct a base and research its exclusive capabilities. A player could choose the base if the team didn't currently have a base, hadn't had one recently killed, and the player had sufficient rank. Picking a base didn't affect the quality of other ships (there being no research or resources...), or affect the quantity of others any more than picking any other ship (in so far as each player could only control one ship at a time, regardless of ship type). They're sufficiently strong that coordination is normally required to kill them, and they draw significant attention from both sides. Given time, they can move anywhere around a map with fewer worlds than larger Sins maps -- ten planets per side -- and where there are *no* fixed defenses of any kind; no hangars, no minefields, no phase-jump inhibitors (it's an open map, no choke points), nada. And with all that, people still played the game fervently and, excepting the odd newbie who never heard of ogging, teamwork or the like, didn't demand nerfing the bases, and having a base wasn't remotely an automatic victory.
If it's too powerful offensively, that probably screams that there's a cost or ability imbalance, not that it should for some reason be still ultra-powerful-for-the-price but immobile.