I like the idea or more interactive swords! The abilities have quite variable impact, I would probably never surveil if I can cast a spell for free but it does fuel itself.
yeah, always loved the flavor of 'em but disliked a few features: the mana cost, the hard color-based protection, and the fact you had to land a hit to get the effect - which required a hefty effect to be worthwhile, making games unnecessarily swingy.
some of them are fairly 'equal' between the two effects, but others (like the surveil+gravecast) as you mention have different levels of punch. they're generally disparate for two reasons:
1. weaker ability enables stronger ability
2. weaker ability is generically useful, stronger ability is situational or requires setup
every sword has at least one effect that will always be helpful, so they're never dead.