I always pictured the first age solars as being THAT evil, if I'm honest. Ripping souls apart to turn them into threads for clothes ("Sexual deviants are in this season"), snorting cocaine off of kidnapped village girls (that they then murder), rape, mind control and genocide all on a global scale... Those kind of things sound ridiculous and silly to us primarily because they don't happen in the real world. If they did happen, however, it would be disgusting and horrifying. That's part of Exalted's charm, in my mind: the utterly ridiculous and absurd are made plausible in the setting and are played largely straight. And if things such as what happens in the Exalted setting WERE to occur... well, Kejak's reaction is understandable.
... But if you don't want it to go that badly, keep in mind that most canon examples we have of Solars being evil in the first age has less to do with actual malice, and more that they just didn't care about anyone else anymore. That thing where they created a massive wyld area in Creation for a training exercise (Operation Wyld Hand, i think) was because Solars wanted to win so badly that they were willing to throw countless innocents away into the worst hell imaginable just to gain an edge. You could use that to come up with things a Solar would do. Walk a warstrider through a heavily populated city center (or 3) to deal with some threat a few miles away, use a spell that costs every life for 200 miles, slaughter a country to create a shadowland so you have access to the essence of the dead, etc etc.