i think you misunderstand why tyranny is good

with most other government types, when you attack at max efficiency (less than 1/3 of your unit type total) you lose 1% readiness but it takes 2 turns, and running a turn doing anything except a GS, BR, PS, SS, or AB, gains you 3% readiness, so you can get of a large number of hits in with a minimal amount of readiness loss

with a tyranny, it only takes 1 turn to attack, but you lose 4% readiness at max efficiency. so you have a lot of turns that you need to use to regain readiness, this is where missiles, teching, or building and growing comes into play. you can still put out a large number of hits, and have turns to do other things. with the other governments, you dont have as many readiness turns to accomplish other war goals outside of hitting.