I don't think the dumbing down was intentional, either. And I think your explanation is as good as any for why she ended up being portrayed this way.

What always made Graendal PoVs interesting, as written by Jordan, was how cerebral they were. She was a very self-aware character, not something you often see in an "evil character" in fiction from that time. I always feel one of the major losses in characterization in the Jordan-Sanderson transition was how intelligent people are portrayed. Cadsuane was a loss, we don't have any Verin or Moridin PoVs yet, Siuan seemed less intelligent, and so do Egwene and Rand, though to lesser extents, probably because they got more "moments of awesome" to take away from their slightly reduced intelligence. Elayne is not given as much of a chance to think about things and speculate...

As you pointed out with Graendal's thought process on encountering Ramshalan, you can see how Bandon struggles a bit in how to naturally write an intelligent person reaching a clever conclusion.

Contrast that to how Jordan wrote Romanda realizing Halima was a Foresaken male channeler. There's gentle buildup where we're exposed to the way she works things out, and when she does reach her conclusion, it isn't a sudden intuitive leap. Instead, several things peppered throughout the chapter fall together.

My early insistence that Graendal was alive came from how RJ wrote her. No way would she be totally blindsided by Rand's "brilliant" plan. I suspect, though, that this was one place where Jordan wrote the expected end point, but not the mechanism to reach it, and hence Brandon filled in the blanks.

What I think Jordan would have done is have Graendal make Delana alone weave compulsion. When Graendal figured out what Rand was up to, she and Aran'gar would have escaped. Then, Graendal would have been broken/mind trapped for her failure, and Aran'gar would have been given the task of killing Perrin.

For Graendal herself, I think the role RJ envisioned was different (and I think we'll see this in aMoL): She will be Moridin's pet consultant. There's nobody else who can begin to understand the man that Rand has become. Graendal is the only one, per Semirhage, who has occasionally achieved reintegration in people who hear voices from their past lives. I think we'll find out that she is the one who pointed out to Moridin that if Rand has all of LTT's memories, then LTT's past feelings for Meirin Eronaile, added up to the sane Rand's penchant for saving women in trouble works up to a way in for the Shadow to get a hook on the Light's Champion again. I think Rand's reintegration and epiphany in tGS must have severely increased the need for a psychologist in a Shadow, and I think RJ intended Graendal to lose her freedom purely because it didn't make much sense that she would give useful aid to Moridin unless she was under his total control.