I could see potentially lowering the duration that they are out, but one thing you may not know about wormhole is that you can melee the worms, which can reposition them unfavorably for the caster, and in some cases, effectively nullify them. E.g. using Tetherball on a worm will spawn the ball inside of the worm, teleporting the ball, and pulling the 2 ends of the worm together; or charging up your Compound melee on a worm; or picking a worm up with Sustain or Geyser and tossing it out of the map, killing anyone who goes back through it (on air maps specifically). Additionally, if someone is hiding behind a wormhole, you just need to throw your spells into the other worm as the spells will travel through and hit them, and then you're thinking with Portals.
I agree it has some unique and substantial upside, but it's also one of the few movement spells that can be countered/nullified by anti-projectile defensive spells when cast: deflect, pillar of fire, rock block, vangua...
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