For example, it made no sense to me that Graendal's spies in Rand's camp (who are they? This would be an interesting question) revealed the relatively insignificant detail that Nynaeve was a great Healer, but did not mention that Rand was on edge, likely to kill women, likely to use Balefire, etc. I think RJ would have had Graendal hear all that, and figure out what Rand was up to the moment Ramshalan came to her, which would make her use of Delana and Aran'gar make sense.

Who taught Delana compulsion is an interesting question. Could it have been Moghedien, after she was tamed to Ishamael's leash? It could have been done in TAR, since we know Delana has had Dreams where Aran'gar's name was mentioned to her.

As for compulsion itself, I don't think it always works by opening the person's mind to suggestions/make them adore you. If Graendal's worst compulsion wipes out personality, it needs to do more than just make the person receptive to her suggestions. And various people like Lanfear and Sammael have confirmed that Graendal does this stuff. So that part of it I can accept. Also, Graendal does indeed have Delana and Aran'gar give Ramshalan random instructions, so there was a verbal component to it.

And while I like your outline of what should have happened, I think this works fine too. RJ may well have intended to have us spend some time thinking Graendal is dead, and Aran'gar as well, maybe, only to have us later see that this isn't the case. What Brandon got wrong wasn't the broad strokes of the way he handled this but the minutia.