Dyvim Tvar said:
Assuming optimal aiming point of of 10 inches from the back of the Slann, a single cannon shot against a Slann in a non-TG infantry unit has about a 1.9% chance of killing him outright (2/3 chance to hit, 1/6 get through Look Out Sir!, 1/2 get through the ward, and 1/3 do enough wounds to kill).
Multiple cannons and multiple shots obviously increase the possibility of it happening, but against 1 or 2 cannon I am more than willing to take the risk, especially since I generally have plenty of option for quickly taking care of war machines.
Also, if running the Slann in a skink unit causes him to be targeted by cannon, to me that's a pretty good thing. The chance that he gets hurt is so miniscule, and it means that my opponent isn't shooting at other expensive stuff he can kill much more easily (like a Steg or Basitladon).
As with everything, this game is about luck. Sometimes, people just strike it lucky, and win the game on virtue of that, and nothing else.
I've seen a unit of 60 skeletons kill 25 Swordmasters by themselves, with no magic at all to support them. That happens. It's RIDICULOUSLY unlikely, but it happens. And suddenly, the game changed significantly because of that.
You can only do so much to skew the odds in your favor. At some point, tactic just doesn't matter anymore, because the entire game was decided through a series of unfortunate events, that, however unlikely they are, means the game ended just like that.
A fun story I heard from my local group, which is actually recorded from a tournament my local group held. VC vs Wood Elves. VC start, decide to raise dead. Miscasts, gets sucked into the warp, and then half his army crumbles right then and there. He lost practically everything, rolling almost purely 10+ on his leadership rolls.
Wood elves turn, nothing of note happens, moves forward, puts a few arrows in him, nothing spectacular.
Next turn, a new necromancer takes over. Tries to use invocation of nehek to raise a few of his many casualties, miscasts, gets sucked into the warp, and even more of his army crumbles. He calls the game right there, having already lost a good 70% of his army, and his last necromancer wouldn't really do much to help this train get back on track anymore.
There are a lot of benefits to throwing a Slann in a TG bunker, but don't do it for the cannon protection. If that's the only benefit you see, you are far better served with a skink bunker.