Blizzard screws the Loyalists over in Shadowlands

[Combatbutler]

Yes, but she does not say that because of the size of her sister's army. It's because Sylvanas has an army of undead, which is immune to the Old Gods corruption, which is also the reason why Icecrown could be build from Saronite, the very blood of Yogg-Saron.

Undead are not immune to the whispers of the void, the lich king binding the corpses is what made this all special, there are undead among the twilight's hammer cultists.

The mere thought that Sylvanas can have such a huge advantage is ridiculous. But let us say it is true that in pure numbers she has the advantage. So what? We have all the heavy hitters on our side. Jaina, Talryssa, Alleria, Turalyon, Anduin and every other big name of Horde and Alliance combined. Those are easily worth hundreds of footsoldiers. Jaina alone could freeze an entire battle field or a giant patch of open sea not to mention her flying ship, while Anduin could revive and heal every soldier that falls.
Sylvanas has herself, Nathanos and that is pretty much it. .

Still Alleria says this and is not contested on the matters, only that Sylvanas has to die, because she will not use that army to save them. Such is the narrative as ridiculous it is.

Even with her new Jailer powers she can't hope to stand against this onslaught

Considering that she just waltzed into icecrown and some of her henchman later take out half the cast, I disagree.

[Magister of Quelthalas]

Good. Sylvanas deserves to die.

[Raisei]

Considering that she just waltzed into icecrown and some of her henchman later take out half the cast, I disagree.

On this you are probably correct. Sylvanas after all carries a plot armor that would make Sargeras jealous with it's size. She has been shown to now effortlessly beat an army of undead and the current Lich King. In a fair fight this wouldn't happen, but she has to be built up. After all she will kill/trick the Jailer soon to take his power.