Hm...Would it make sense to, instead of offering up an aspect tag on that freebie the grapple offers for the +2 to hit, let someone tag it for the effect of not letting the target defend with one particular skill? Going back to the speedster example, if you've grappled him in the hopes of holding him down long enough to hit him, could you have the grappler put a temporary aspect like ARM LOCK or HEADLOCK and have the punch-thrower tag it to say that he couldn't use his Athletics to dodge that one attack, but instead had to use Fists or some other applicable skill, rationalizing it with, "Well, I'm holding him down, so he can't sprint or backflip out of the way"?

Because that +2 on the temp aspect can be done a lot easier and quicker without grappling in the first place--why A. create a temp aspect, B. tag it for the grapple, and C. put on another temp aspect to tag--and risk the target breaking the grapple anyway--when you can just go A. create a temp aspect, B. have your buddy tag that to punch?

Weak attacks can rack up stress that slowly whittles away an attacker - this is something I did recently, where I eventually just ran my opponent out of stress boxes entirely - we both had strong defenses, but I didn't have strong attacks.  Weak spells can set up maneuvers (eventually leading to strong spells) or whittle away at opponents with attacks.  Weak blocks just do nothing.  And personally, I'd really prefer a game system where you aren't limited to just the tactic you're best at, and where non-combat characters can still make small but useful contributions if they do end up in a fight.  Maneuvers are one option for this sort of thing.  I would prefer for blocks to be another.

Apologies, I meant a weak attack roll. As in, if you can't reliably get past a defense to cause those shifts in the first place.

And I agree with Sinker, I think: A block would set a difficulty of something that normally wouldn't, and affect the outcome.

My question is, does this count for defenses? Like, if you've grappled a speedster (Let's say, Athletics at 5 with Supernatural Speed) specifically so that an ally can gank him while he's pinned down. Now, in my mind, if you've got, say, a 4 strength grapple on him, should he really get the full benefit of his 7 dodge roll? It makes more sense to me to apply the block as a penalty to that as well--he'd still get the dodge roll, it'd just be reduced because of the block. (Thinking of, say, Goku and Piccolo vs. Raditz here).

I would argue it should need a stunt, because reversing a grapple isn't something you'd necessarily be able to pull off as easily as establishing one. Anyone can just wrap their arms around someone and hold tight, but it takes some skill and technique to not just break a hold but to turn it around on your opponent. Plus, as mentioned, to establish a grapple you're supposed to invoke or tag an aspect--having a stunt effectively takes the place of that.

I think it's fine to get rid of a Mortal stunt, particularly if it becomes redundant. For example, one player in a game I'm in has Takes One To Know One, so his character can use Deceit instead of Empathy to detect lies. Eventually, he plans to boost Empathy once he's got a couple more skill points to spend, at which point the skills will be equal, making the stunt effectively wasted space.