Every time, when you build up a Zone of death, teleport is bad for the gameplay.
Let it be a necromancer with alot of zombies, let it be a Druid with vinesnappers and thornlashers, let it be a priestress with a bunch of knights. If your mage is teleported into this hellhole, there is often no escape possible (jinx, another teleport, tanglevine etc.). Your mage just dies there. And btw you cannot save your mage with a nullify, if your opponent uses his qc and action at the same time (seeking dispel, teleport).
I personally agree that there should be something that prevents this situation or makes it happen not that often. Especially in 2on2 games, teleport as it is now is the spell, that takes some fun out of the game.
"You shall not teleport enemy mages" could be the answer. Something else could be "if you teleport the enemy mage, pay double mana cost"