I only say that you don't seem to understand pulp fantasy because it sounds like you're complaining that he is so powerful. Either that or you're complaining that he always wins in the end; I'm not sure.
These aren't 'tropes, and they aren't bad writing when taken in context. They're simply how pulp fantasy 'works'.
All pulp fantasy protagonists beat the badguy and save the day. It is not a particularly subversive genre. The difference between a good protagonist and a Sue is that the the former is a human character who screws up, has limits, and acts like a human, while the latter is just a hollow self-insert who doesn't do anything -except- succeed, and who's 'struggles' with the antagonists are thus far less interesting.
The only legitimate criticism that I've read, was >>6394289
I'll admit, Mystra's favor IS the sort of blank-check superpower that a Sue would have, but that's not how it actually used. When some angel-princess sue has that kind of power, she uses it to resolve every serious conflict, resulting in shit writing. Mystra's favor, conversely, is used as an excuse to let Elminster fail without killing off the character. He'll blunder in over his head and fail, she'll whisk him away, he'll try again and win the day without her help.
In Elminster in Hell Greenwood almost seems to be parodying the Mystra thing (even though it's a different Mystra now) by having her TRY to storm in personally and rescue her mancandy by brute force, only to FAIL, forcing the godamn goddess of all magic to find a backup plan.
This is one of the reasons why I disagree when you say Greenwood writes the character the same as everyone else. He's very self-aware, and if anything a little -too- apologetic, going out of his way to try to prove that Elminster isn't perfect.