I will get more in depth on this later, here's the bare basics of how the grenade-yomi works.
Sonya's grenades are around +7-ish on block. Throwing the grenade and detonating the grenade are two entirely different things.
If she detonates the grenade while still in the recovery frames of throwing the grenade, she may have +7 from the grenade, but if she still has 14 frames left in her recovery animation for throwing the grenade, she is going to be -7 instead.
So, first. Yes, if sonya want's to be + after a b14 xx Grenade throw, she has to wait till the end of her throw animation to detonate to be reasonably + on block. This DOES leave a gap. However, simple pokes in the gap are going to trade with a stun grenade- Sonya wins that trade with an easy conversion for a full combo. This leaves armored launchers as an issue though, but they aren't free 'get out of jail' cards against stun grenades. Sonya need only delay the detonation so the armored reversal loses it's armor by the time it detonates. Example vs Kung Jin:
(I picked Kung Jin as an example, seeing as he's the prototypical example of a character who has alot of strength in armored launchers. But this may vary with other characters):
So what happens? Well, if Kung Jin does his spin early, the armor will run out just before the grenade detonates. He'll get the first few hits of his launcher, but will then be hit out of it by the grenade before Sonya is actually launched. Then Sonya converts for a a proper combo off the grenade.
But what if Kung Jin delays the armored reversal so his armor kicks in as the delayed grenade detonates? Well, if he does that, he has to delay it enough such that Sonya can block the reversal in time. Safe. The same situation happens with b33 starters:
Same situation. If he reversals early enough to "punish", the armor runs out before the grenade detonates. Sonya still stuffs him. If he delays long enough for his armor to active just before the detonation, thus absorbing the hit, Sonya has recovered enough by then to block it.
HOWEVER, this can be blown up. It's not free to blow up, but there are ways. For example:
So in this case, Kung Jin can start with a normal to punish, and THEN go into his armor. The normal hit soon enough that Sonya can't block it, and since it is canceled into the armor, it kicks in just at the right time to make him safe from the detonation.
But to be clear, that's not free either. This is only when Sonya DELAYS the detonation because she's fishing for + frames. Since Kung Jin needs to start with an un-armored standing 1 in this case, if Sonya goes for an early detonation instead of a delayed detonation, Kung Jin will be completely stuffed and eat a damaging combo.
Despite the gap, grenades are still great for pressure tools. It's just not absolutely free pressure. Here's one example, just a simple one:
And here's another pressure example, one that I used to demonstrate how + a grenade is if it's detonated at the end of her animation. Remember, an opponent who has meter still needs to take significant risks to blow this up, they can't stuff it for free. An opponent without meter -or who doesn't have an armored launcher that leads to good damage to make the risk worth it- is REALLY screwed
Sonya's b3 is 14 frames, and her d3 is 7 frames. So this trade indicates this detonation is around +7 on block. I was very thorough to ensure my timing wasn't off.
Now, there are other give and takes to delayed detonations. Even if an opponent has no good way to outright stuff a delayed detonation, because they don't have a good armored launcher for example- delaying the detonation often means they can jump out of the pressure or backdash. It's just up to the Sonya player to be smart about her options, and her opponent's options. That's not too much to ask. Grenades are still good, even if they aren't a unilateral "free pressure" button.