Well, the Tholians dragged the USS Defiant not only through time, but from an alternate reality too. Defiant went from the Prime TOS to Mirror ENT.
1) These aren't Mirror Universe Ambassador-class starships.
2) Cryptic has greatly overused the Time Travel and Mirror Universe to get ships, thanks to the Temporal Lockbox and the Mirror Universe Ships.
Originally Posted by mandoknight89
It's a known issue with the Ambassador-class. Why else do you think Starfleet went back to the Excelsior for its workhorse heavy cruiser instead of the later Ambassador?
And you think the Excelsior's Transwarp Problem was bad.
If you read Doug Drexler's pictorial on the Enterprise-C, it mentions that the nacelles look oversized for the ship. Comparing the STO screenshot to the Memory Alpha picture, I don't think there's an appreciable difference in proportion.