Sallies are our only real artillery. And they need to get fairly close to do their work, and that work tends to be limited to screwing with T3 or lower dudes. Any higher, like Chaos Warriors or Ogres, and the wounds will be few enough to hardly warrant his imminent death soon after. I know they are strong but we have a thin codex as is, not a lot of diversity. Most of our options are darn good, like our Slann, but it is part of a cohesive working whole, and take parts of it away and the army starts to have glaring weaknesses that would take a strong army and make them an ok army. Cupped hands, the disciplines, they could use some cost and usage changes. Fix that, and the slann is, imo, just fine. Hell, he's just fine as he is now, to me, but that's because as strong as he is I don't always win and lizardmen don't always win. Outside of a perfectly balanced environment where everyone has an exactly equal chance of succeeding statistically, someone is going to be strong and someone not as strong. You don't have to neuter them. It is just the nature of the game.