Which is better, Sorcery or Knowledge?

Still, mages often have very little mana, so you can't make a good Chaos or Summoning mage, even though they often get Summoning spells.

Again, it all depends on the game you're playing. If it's a small map for 3 game weeks, that's one thing, but if it's a mega-sized map for 2-3 months, that's a different situation. You shouldn't literally compare a mage and a dungeon because they are different things. A dungeon is predisposed to Chaos, and as a result, its racial abilities are tailored to this type of magic. A mage is completely different; ideally, a mage is strong because of the minor artifacts on the troops, and they, in turn, are tied to his knowledge. I assure you, a Light mage, with offensive/defensive units, experience protection after 2 months of play with troops under minor artifacts from knowledge for 30 is overpowered; the main thing is to create minor artifacts not randomly, but taking into account the opponent's capabilities.
P.S. This is not the first time I've encountered an outright underestimation of mages, but in online tournaments, a mage is considered one of the most inconvenient opponents