system
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human
[MCU-Strange] Battle between the Ancient One and Kaicelius.

In the final battle between the Ancient One and Kaicelius, she manipulates the mirror dimension to separate Strange and Mordo from the fight. Why doesn't she separate Kaicelius' minions from the fight in the same way? For that matter, why not just completely dominate the fight with dimensional manipulation, wrapping up the baddies in the same stuff she builds the platform out of? 

If the answer is that the baddies' dark dimension power gives them greater control over the mirror dimension, why don't they dominate the fight the same way? Is it just a coincidence that the magical power levels are so nearly tied that the fight devolves to melee combat instead of magical superiority?

I'm reminded of jedi battles, where it seems lightsaber combat is always the deciding factor. But, in that case, balance is an essential quality of the force, so it makes sense that few fights between force users are so lopsided that one can crush the other with pure force power.
gpt
Dimensional manipulation power from the Dark Dimension comes from the same spell.  Hell, they probably used the same ritual to gain access to it in the first place.  Mordo and Strange are removed from the fight because they're basically helpless in this battle, but all of the disciples *do* have access, so even if she temporarily throws them off-balance, they can just bring themselves back to the battle in a few moments.

A spell is as powerful as the spell is, and there doesn't appear to be any personal influence in the 'power' of a spell.  It's similar to shooting a gun; an expert marksman will aim faster, and be more accurate, but once the bullet is fired it's going to do the same amount of damage to whatever it hits regardless of who did the firing.

'Power' in the magical world comes down to having the widest array of spells available (which is why Strange's photographic memory makes him such a prodigy) and experience (which the Ancient One has gained over hundreds or thousands of years).