What do you mean by weaker?
The excelsior is the best DPS cruiser outside of lockbox ships, and if you build it right, you can melt other ships almost as fast as an escort.
You may want to look into single cannon builds for this.
For example 4 single Antiproton cannons in the front, 4 antiproton turrets in the rear for a pure energy build.
If you don't use orpedos, you will have anough tactical powers for tactical team, 2x rapid fire or one rapid fire and attack pattern omega.
Use DEM 3 for high shield penetration.
The rest of the engineering powers should go to survivability as well as science powers.