Well let's use a good example here to get at the question the OP is asking.
First, to the OP, it's generally assumed that you'll be putting a specific block on everyone in an area (say, a block versus movement, resisted by might, by turning the ground into quicksand with a potion that I just listed on another thread), OR, a block on one person, which can block EVERYTHING they are trying to do, depending on context.
So let's give it good context: The block is a mental attack, fogging the character's mind so that he takes no action. Despite the lawbreaker implications here, this clearly should block any type of action the character might take. To give it some stats, we'll say it's applied at strength 8 and lasts 3 rounds (because the caster somehow spent 10 shifts on it). So, ANY action of ANY type attempted by the victim suffers and 8 strength block, until something breaks it. And we'll say that the target got a chance to resist with discipline at casting.
That's more than normal grappling does, which isn't going to shut down everything (just close to it. It interferes with spell-casting, which can be done purely mentally, so there. But it maybe wouldn't interfere with, say, using knowledge skills (which means, making declarations and such).
Our spell now does that as well.
So the only thing left is: should it require invocation of an aspect to place, like a grapple?
My answer is no, because it's magic. This isn't logically inconsistent; it's just a different set of rules. The grappling rules have that provision to make it a little harder to grapple, and to reflect the need for getting into position in some way. This is needed because grappling quickly becomes a "win" button in most games, and because it's hard to break (a non-grappler is going to have a hard time breaking it). However, our spell can be broken by ANYTHING, so the victim can just default to his highest skill and roll that to try and get free. Thus, it's easier to break than a grapple. Also, while you can add duration via a second "spell", the caster is still burning through mental stress quickly to keep this up... thus it cannot be sustained as easily as a normal grapple.
So, really, you're looking at a different set of rules (magic vs physical) and, truly, a different effect with different strengths and weaknesses. Despite the similarities to grappling, I see no reason to impose the "need to invoke an aspect" rule on such magic blocks: they already take more to land, are broken more easily, and can't be maintained as long as normal grapples.
