It depends on what time period the Empire is in when they fight the covenant. So saying there is no esclipse is completely wrong. The only reason it was ever destroyed was Luke and Lea were able to reverse the force of the new emperor and it destroyed the esclipse.

AT-AT armor can withstand magma according to Thrawn, lets see a scarb survive that. A covenant Capitol ship compared with the Imperial Star Destroyer is a terrible match. The ISD(55 turbo lazers, ion cannons and many other attributes) has much more fire power than most covenant capitol ships which explains how hard it would be for a covenant capitol ship to ram an ISD.

This is not necessarily a battle between capitol ships. This is also a battle of other space vehicles. Broadside cruisers have very longranged boron missles that are devastating to space stations and frigates. The tartan patrol cruiser would be a counter to Seraphs because it is designed to take out small fighters and it is 200-600 meters long equipted with lazer cannons.

Tie defenders are very maneuverable fighters with ion cannons, lazer cannons and proton torpedoes. Even if there is not a lot of them they could take down several covenant capitol ships before being destroyed due to its maneuverability and shielding.

Clone Commandos would give the covenant a fit. There like another master chief but in more numbers. Imagine what over a hundred commandos could do.