The Empire is a lot more competent. Palpatine knows how to stay in power.
The Death Star is an impenetrable fortress without exhaust port, tight security makes sabotage almost impossible. Yavin 4 is blown up and the rebels scatter in all directions. Imperials have more versatile fleets to combat the Rebel insurgency, mostly fighters and frigates while the capital ships get point-defense systems. Stormtroopers are now professionals and deadly, no more making fun of their bad aim and clunky armor. They are the elite corps of the Imperial Army, made up of veterans of the Clone Wars. Their armor absorbs energy weapons and they have camouflage (no more white in deserts and forests). Ground vehicles are more like those in the Prequels(more functional) and armored divisions always advance with infantry support. Every time rebels fight imperials in the open, they get obliterated. That’s why they have to use more guerilla tactics, no more decisive battles.

The Empire can’t finish of the Rebellion, because they have to deal with an Outside threat which ties up most of their resources. (The only thing that makes sense)

Lightsaber combat is the noble way of combat by the Sith lords and Jedi knights, its martial arts choreography is inspired by historical swordfighting. It’s intense, but not over the top.

ideas:
-Not all the Jedis have been purged and there are more Siths(maybe an aristocratic class?)
-Are the Jedi a new religion which threatens the Empire? Maybe there are several sects of force-users.
-The Old Republic didn’t last thousands of years/generations and Imperial rule was longlasting
-Luke becomes the new Emperor after beating Palpatine