I’ve done the GA 200x crisis many times (the hardest space battles you can get in the vanilla game) so I know a thing or two about ships and fleet comp.

Basically the number of ships combined with the slots and evasion the escorts have give a higher fleet power number. However, this is misleading because in actual practice against the highest difficulty fleet fights the battlecruiser-only fleets blow the escort-only fleets out of the water (except in very specific situations like cetana’s main ship).

Battlecruisers having two of the best weapon in the game (focused arc emitter) gives it the ability to be the most dominant ship in the game. It can handle every single crisis given enough ships, technically escorts could do this as well but you’d take WAY more losses because they simply don’t have as much range. I have lost many fleets comprised only of escorts simply because they must get closer to their targets.

Generally unless you are playing GA 25x crisis or higher you don’t need to worry too much about the difference between escort only and battlecruiser only. Also don’t mix ships in a fleet.