I think you have it figured out, if the grappler plays any rune, the counetr is any rune, but if it's a specific Trait for the action, then the specific Trait needs to be matched. I think that scenario is a great laugh, and I'm sure everyone has smiles around the table - which is the goal of your game night. But before it gets old, here are some options:
- The grappled person can still fight back and attack, and the grappling drake may have to forego parry.
- The grappled foe can also play a rune to grab onto the drake, before the talons let go.
- The grappled enemy can perform some out-of-box cinematic actions like tying a rope around the dragon, tethering themselves.
- Give your denizens powers like Aura or the ability to drop 4 intensities of impeded on the drake
- Be truly diabolical and make use of powers like Dark Juxtaposition

All in all, it's great that your players are being creative. Don't stifle it, make sure to reward it.