system
Given the following post, respond as if you're commenting on Reddit:
human
[Mage The Ascension] How powerful is a Master Rank mage?

Master Rank mage who has achieved 5 dot mastery in one discipline, or even all of them. Do they even compare to oldest vampires?
gpt
A mage who has achieved master rank in all Spheres is effectively a god to most supernatural beings- there are few statted up beings that can rival them in the world of darkness. One who's achieved mastery in just one is still very powerful, especially since they likely have high dots in other spheres

The main issue is that a dot in a sphere buys a *lot* more then, say, a dot in a discipline or a gift or an arcanoi or what have you. Most supernatural powers give you one specific power. For example, a vampire with one rank of dominate can give a one-word command if they look into your eyes. A lot of possible uses, but still one concrete power.  
Conversely, a mage with one dot in the Mind Sphere can sense mental traits, scan auras, read emotions, see the near umbra, detect lies, protect their own mind from influence, absorb data at a superhuman rate and boost their own intelligence. And that's just as sample powers.

This continues: our Ventrue has, at 5 Dominate, 5 discrete, fairly focused mind-controlling powers. Our Ecstatic with 5 Mind, meanwhile, has just a laundry list of abilities to sense, alter, boost, degrade, control, destroy and create minds. And that assuming they can't combine it with other spheres for even more abilities, which they likely can. A mage increases in power *massively* more quickly then anything else in the world of darkness.

This is a real problems with crossovers. With the exception of the real heavy hitters like  Antediluvians and Incarnae, there are very few beings in the world of darkness that can stand up to a mage of equal "level". They simply get too versatile too fast.