I think there's an issue with your math though, You are assuming that someone would actually take 5 skullcrusher
It's true that I have yet to face anyone running more than 4 skullcrushers in a unit, at that point they usually break them into two units of 3.
First off, I wouldn't say that is an issue with the math. Secondly, you are correct that you seldom see more 4 skullcrushers in a unit. However I don't think it is fair to compare a 410pts unit against a 332pts unit. Also I've personally run a "deathstar" unit of 7 skullcrushers, they delete everything they touch. But I admit that it is
not an ideal setup.
but you are also off a bit on your math, juggernaughts are not frenzied only the rider is.
You are absolutely correct that the juggers themselves are not frenzied, only the riders. However I did not assume that the juggers were frenzied in my calculations. The riders have two base attacks on their profile plus one for being frenzied. The juggers have
3 base attacks on their profile.
I also do not believe they are guaranteed to get a charge due to being frenzied, good use of a block of 10 saurus to force an overrun or pursuit can set you up wonderfully.
I have to agree that a skullcrusher charge is far from guaranteed. I would say they have a greater likelihood of getting the charge, but movement, positioning and generalship will probably play a greater role. I was following along with the example you originally posted where you stated that the Skullcrushers had the charge. But I agree with your point.
Another tactic is to deploy 2x4 instead of 4x2, MI win all day long with supporting attacks so reducing frontage can sometime really pay off, it also forces the WoC player to split his attacks against your champion and normal krox which turns some things around.
That's an interesting tactic, with such a small frontage the skullcrushers could only manage to get 3 models into b2b contact. That would leave the kroxigor with 13 attacks against the skullcrushers' 19 attacks (or 20 attacks if we assume a unit of 5). This will help the krox out a little, but they are still going to lose the fight. Additionally, it does open up a really juicy flank.
And always remember if that is one of your priority matchups then just slide that scar vet into your krox during deployment, still highly mobile and does very well against most Krox targets.
I don't really think it is fair to throw a character into the mix. As good as our characters are, WoC can serve up better ones. In my opinion the "Hortennse" unkillable lord is arguably the best character in the game.
but I do have at least 2 wyssans to cast and I almost always can get at least one off in a pinch, that changes the whole numbers game greatly. It is almost shocking how much better krox do to crushers with a wyssans.
Just as with the addition of a character, I don't feel it to be a safe bet to assume that you will get a boost from magic. I don't doubt that Wyssans would make a HUGE difference, but at the same point we could assume that the WoC player throws a purple sun through the Krox unit. Your opposition has just as much of a chance (or at least nearly as much, since the Slann is superior magically) of using magic to hex or buff or attack to gain an advantage for his/her side.
To illustrate the point of this matchup, lets take a look at a situation where the odds are stacked against the Skullcrushers...
8 Kroxigor + ancient = 410pts [formation of 2 wide and 4 deep]
4 Skullcrushers (ensorcelled weapons) + standard + musician + razor standard = 377pts [formation of 3 wide, 1 crusher in the second rank]
For the sake of argument, let's assume that neither side got charge, it's an ongoing combat
3 Skullcrusher Riders attack (3 attacks each @S5) = 9*(2/3)*(2/3) = 4 wounds
1 Skullcrusher Rider supporting (1 attack @S5) = 1*(2/3)*(2/3) = 0.444 wounds
3 Juggers attack (3 attacks each @S5) = 9*(2/3)*(2/3) = 4 wounds
Total wounds = 8.444
4 Kroxigor attack (3 attacks each [4 for the ancient] + 2.2 via PF @S7 ) = 15.2*(1/2)(5/6)(2/3) = 4.22 wounds
Total wounds = 4.22
So the difference in wounds is 4.22 in favor of the skullcrushers. Let's round down that to 4 and add 1 for the standard. The kroxigor just lost by 5. If we look at this in a vacuum, they need insane courage to hold. Best case scenario, they have a leadership10 BSB Slann in range, and they have to make a re-rollable leadership 5 cold blooded test. Even with everything being stacked in the Krox's favour, I don't like those odds.
Please note that I did not include splitting attacks between the krox ancient and the unit for mathematical simplicities sake. It would not make a big difference either way.
Add to this that skullcrushers are far resistant to spells and other match-ups and it is a really big uphill battle to say the least, IMHO.