Well, in the Honorverse, the Solarian League did have the "most powerful" fleet, technically speaking, by virtue of its sheer size advantage - IIRC, the SLN has something on the order of 2.5-3k dreadnoughts/superdreadnoughts on active service with another 8-9k+ dreadnoughts/superdreadnoughts in mothballs in their Reserve. If they massed them all together, they'd be able to roll just about anybody under through sheer numbers. No idea how many lighter ships they have, though.
That being said, the SLN is (apparently) the most technologically conservative fleet in the Honorverse. Unit for unit, the SLN's DN/SD fleet is the weakest (their smaller ships tend to be more technologically advanced than their larger brethren) but when you outnumber the enemy by 4 to 1 (using the pre-war Havenite numbers - said to be the second largest fleet in existence) in active service units, and outnumber them 22 to 1 in total (theoretically), nobody's really going to mess with you. As such, the SLN can get away with having relatively crappy dreadnoughts and superdreadnoughts, since they don't see that much action.
The Sollies thought that they were better than everybody else (not invented here syndrome), but even "obsolete" Manticoran/Havenite units are more advanced than their "modern" Solarian counterparts. Non-Sollies with equivalent or superior capabilities simply chose not to enlighten the Sollies.
Here, though, the UTC is both more technologically advanced and (presumably) larger than everybody else (except possibly the Souri). Similar in some ways, but different in others.
That being said, I'm interested in what these "revelations" are that are the official reason(s) the UTC is getting involved; and, of course, the real reason(s).
Surrendering their vessels? Damn, but that's not gonna happen. I could see standing down and backing off, but not outright surrender.