That's why Repulsing Capitals seems like a tricky issue. Right now I've used it to cut off a Capital's escape and push it away like the other ships, but if it weren't affected it would seem very easy to just envelop the Capital with my fleet, then just smack Repulsion on and suddenly the Capital is all by it's lonesome. It would still retain it's ability to retreat though, something one being ping-ponged around by Guardian's loses as it waits to die.
Upon thinking about it though and with some more experience, I don't think Capitals should be affected for an unrelated reason. I use Guardians and Repulsion mostly to defend my higher Capitals, because Malice and Cleansing Brilliance is one of the most useful things in the game. Alone, I think either the Repulsion or Malice and Cleansing Brilliance combinations are balanced and counterable.
The Malice and Cleansing Brilliance requires two high level Capitals to work together (either of which can be disabled by a single Capital of lesser level, or focused fire on by much less valuable ships and killed) and it requires more ability than just drag clicking your Heavy Cruisers, clicking on a target, then watching it die. It allows Advent's inferior economy and production capabilities to compete with the superior numbers of ships it will face. People may not like it, it might be unfair to Vasari and TEC since they don't have the same technology, but they have some very mean abilities of their own. There are other threads to argue these points more, but this topic is for Guardians and Subverters, so I'll leave it at that. Strong, but counterable.
And Repulsion can be beaten by massed LRMs or perhaps strikecraft in some situations (although they are still in dire need of improvement). It's annoying, but as has been said, it's not a game winner, just a game staller.
But here is where the the synergy comes in.
The Guardian's Repulsion outranges many of the disabling abilities of enemy Capitals (all except Reviere, I think). So a good player that knows that one of the two ships in the Malice and Cleansing Brilliance duo-of-death have to be stopped can be prevented from even doing that because of the Guardians. So in the absence of a ton of LRMs they will be forced to not only have the frustration of the Guardians, but also get the Malice and Brilliance combination wielded against them while they can do little to combat it.
And that is unfair, if they're smart enough to see the ability coming and build a Capital (or multiple Capitals) with the express purpose of disabling the combination, they should be able to and some little Cruiser shouldn't stop them dead. What if the Vasari could make it nearly impossible to kill their Phase Gates, or the Sova could outrun all of your other ships? Guardians can make one of the faction's greatest strengths a bit too strong, depriving the others of what would otherwise be a solid counter-tactic. It's a combination of three different ship types all working in tandem and does require some ability and micromanagement, but I think it's too big a game tilter in the right hands. I have only used this combination myself, and have not had it used against me yet, but I expect such ideas to catch on as more people get used to Advent's toys.
Advent has gotten much more popular since the patch, and I've used or had used against me Repulsion a good number of times even since my last post, but here's what I currently think...
-Reduce it's slightly range while slightly increasing the range of all LRMs, so that LRMs can all effectively counter the tactic. It should always remain a good counter to Heavy Cruiser spam (at the very least to encourage mixed fleets) but Vasari and Advent now have a rough time even with a mixed fleet getting close enough to the Guardians to do damage.
-Disallow the Guardians from pushing targets too far out of the initial circle, I had one Guardian knock a Halcyon easily a good 10,000-12,000 game distance last night while preventing it's escape from the Gravity Well, I thought perhaps the distance knocked outside the circle was based on ship size or something, but that didn't even seem so.
-And don't allow Capitals to be affected by it. This will make Capitals vulnerable to being surrounded and cut off, but at least they won't be simply out of your control if an Advent starts micro'ing to coral your ships. You can always run away, and this makes countering the abilities of the Progenitor and the Radiance that may be lurking inside the Advent fleet possible.
Although multiple suggestions, I think they're all light enough by themselves to not risk sending the unit to the doghouse (reactionary over-nerfying really hurts most games I've played, incremental changes are usually the way to go, from my experience). If they're not enough though, the idea of expanding the range of Sabotage Reactor and Steal Antimatter I think is a great way to give the Light Frigates some more use the game as a whole (they hit obsolescence the moment the first LRM roles out, typically). The Subverter would need tweaks of it's own to fill the same role, but I'm no expert on them.