I think there's autoguard when doing one of the combos too, not sure if it's charge A - X or normal X combo.
As for frenzy Tigrex/S. Magala: Yeah, they were tough. Especially the Tigrex. That thing got me bad with its quick turns. Still, it's just like any other monster. Go after it a few times and you'll learn it and it'll be easy.
My latest surprise was the frenzy Brachy. That speed increase is no joke and it even affects the slime.
I'm loving the frenzy effects though, really. It just gives such a nice feeling when you've got the upper hand, then the monster stands up after a short rest and suddenly becomes stronger and especially faster, making you feel like you're way too slow for it. Then you slowly adapt (or don't) and get a real sense of achievement.
I've just beaten my first Monoblos btw. Even more annoying and dangerous than the Diablos. Rage speed is insane, I can't even imagine what it's like in frenzy.
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Also, I've recently started using SnS instead of Charge Blade. It's actually very effective, even on S. Magala (been farming it to upgrade my Magala CB, but it just ain't giving plate and even tail carve keeps giving scale instead of tail). It might be worth a try, the added speed might be what you're missing on CB.
Keeping 1-2 other weapon types in general is a good idea. Sometimes that change in the patterns or reach or whatever is actually an insane difference.