Would you be able to tell us how fast Dragomas is able to transform into a dragon, or would we have to watch/fight to find out?
Because if Dragomas has to spend some time casting battle magic to transform, I imagine the counter would be speed and dispelling, whereas if Dragomas is able to transform nigh-instantly and at will (which seems more likely), that would imply to me that it is possible for other wizards to develop the ability to instantly and at will cast battle magic too. Which I guess would then be the sort of calibre you need to be at to compete for Grand Patriarch/beat a dragon.
Like, if Mathilde got good enough at Pendulum or Pit of Shades to cast instantly and at will I could see her beating Dragomas, and practically speaking those look like feats of the same skill level to me, so makes sense.