Not that this will convince anyone out of their condescending certainty of Valonqar Jaime, but, you know, I appreciate any stimulus for some actual discussion of the theory.
Additionally, I don’t agree with “too obvious” as an argument. Sometimes, a theory is super-obvious because it’s 100% accurate. A popular argument in Harry Potter fandom against Ron/Hermione was that it was too obvious. Yeah, it was obvious because it was absolutely happening. So I don’t support that objection to Valonqar Jaime.
I think a better way to describe the problem with Valonqar Jaime is that it’s giving Cersei too much of what she wants. Wait, what, you ask?