Minbari Tinashi War frigate overall rating: 850. Cannon Source link: 1
Earth-Alliance Nova class overall rating: 1350. Cannon Source link: 2
Earth-Alliance Babylon station overall rating: 3000. Cannon Link 3
Clearly the Earth ships have MUCH higher ratings. This is from cannon source -- B5 wars. The Babylon station is the ONLY Earth ship that traveled back to 1260AD, so knowing the power rating of the Babylon station is KEY in answering this question. Considering the Babylon station has over THREE TIMES the power rating compared to the Minbari Tinashi frigate, I think that answers the question in that Earth tech in 2254 is superior to old Minbari tech from 1,000 years ago.
If that isn't enough, here are also facts from the show itself:
The Nova class was said by JMS himself to be able to dish out heavy damage to a 2250's HEAVY CRUISER -- the Sharlin. The Nova also ripped through the hull of a 2250's era Sharlin Heavy cruiser, taking out their leader. So if a 2250's Nova can do that much damage to a 2250's Minbari Sharin HEAVY cruiser, then a 1260 AD Minbari FRIGATE class ship would very likely be outgunned by a 2250's Nova DESTROYER. (Remember, Earth Nova is a DESTROYER class, while the Minbari ship from 1260 AD is a Frigate class ship, which a destroyer completely outclasses a Frigate). FRIGATE and destroyers are very, very different ships.
Babylon 5 (which had less weapons than Babylon 4) was able to take out a modern day CAPITAL class Centauri Primus, the strongest ship of the Centauri Republic. If Babylon 5 can destroy the modern day Centauri Primus, then how could it not destroy a 1,000 year old Minbari FRIGATE class ship? Is this 1260 AD Minbari Frigate ship also superior to the Centauri Primus? Very, very, unlikely. ALSO: Babylon 4 was even MORE heavily armed than Babylon 5, and much larger! Babylon 4 was armed to the teeth, was miles long vs a 1,000 year old Minbari Frigate? Babylon 4 definitely has more firepower than a 1260 AD Minbari Frigate, and the weapons of Babylon 5 proved how extremely powerful they where against modern days ships (such as Babylon 5 taking out the Centauri Primus). So putting these same Babylon station weapons against a 1260AD frigate class? I think the answer speaks for itself
Earth defeated the Dilgar. The Dilgar defeated even the Narns, where fleet after fleet of Narn ships fell to the Dilgar Military. (read: Dilgar war). So clearly there is no way the Minbari Frigate ship is also superior to the Dilgar ships, and the NARN G'Quan Heavy cruiser. The numbers from B5 wars don't lie, nor does common sense of knowing that a 1260AD Minbari Frirgate ship simply is not on the same level with a modern 2254 Dilgar, Narn, or Earth destroyer class ship.
Simply stating facts, and using the factual numbers from B5 wars. The Babylon station, the only Earth ship brought back in time to 1260AD, well the Babylon station has over 3 TIMES the overall rating as the Minbari ship. Numbers from B5 wars and facts/events from the show itself can give this a solid answer to the question pretty well.
1: http://www.rpgsheets.com/sheets/005092.pdf 1
2: http://www.rpgsheets.com/sheets/005054.pdf 2
3: http://www.rpgsheets.com/sheets/005001.pdf 3