I believe Kotal isn't too bad. His War God is very solid and doesn't need any buffs. His other two variations may not be as strong, but the way I see things, it's a matter of how hard you want to work.
War God = Easy
Sun God = Medium
Blood God = Hard
All variations are viable imo, you'll just have to play smarter and have stronger footsies to use the weaker ones.
Ya, War God is fine because he has tools. For the rest; it's long been proven in fighting games that high damage characters rarely ever place highly. A big part of the reason is that combo's mean "lower damage characters" actually deal
just as much damage as a "high damage" character like Blood god, only they have a mountain of tools to boot. As they are now even though i love them and it makes for great training the other two just are not competitive viable.
This is more of a design issue then a balance one though. If blood god got armor, or if Sun god got fast sun rays or anything else that would give them some extra tools to apply pressure or attacks they would be much better.
Also if you are slightly better then a player who is playing an easy char and your using a hard one, you will have a net result that is weaker then they are. For a Harder character to be balanced he actually needs to be slightly stronger then an easier character, because a player won't eb bringing out the maximum as often.