Not really different to a fighter grappling them.
Some creatures/characters are simply not very well-suited for grappling.
But you can still cast some spells (few enough, of course, unless you prepared them with Still Spell), or escape with a good roll, it's not like the grapple check was virtually unbeatable, as it is with some monsters. Clerics, for example, have
Freedom of Movement to completely negate the spell, or could be buffed with
Divine Power and stand more than a good chance to make the grapple check. Rogues could escape with Escape Artist.
And the damage the spell does is pathetic. It takes ages to kill something with it alone.
Bye
Thanee