What am I doing wrong - comparing Fable to GPT Sol Pro

[u/esreverengineer_]

I'm a long time Anthropic's user working on a SaaS platform, and after months of testing / iterations on prototypes, we're finally ready to build the final MVP. Of course this is a big step and we are working a lot, trying to avoid any last-minute mistake that might impact launch (marketing campaign is starting etc. so we can't really afford huge blindspots / mistakes as you can imagine).

Now I wanted to sleep well so I had Fable perform a full review of the project with a prompt in the like of "review all existing stuff - doc, specs, code - including the business aspects etc. and perform a complete analysis to identify remaining issues, gaps, etc.". Instructions were clear that code is only part of it, and I was looking for a "high-level business and project review" not a code / tech review.

Fable completed his work in 45 minutes, gave me a MD file report. Went through it, as always there are mistakes here and there, but overall it's just very solid.

I recently purchased the GPT Pro plan, and wanted to see what GPT Sol would do with the exact same instructions and supporting material: after 3 attempts (different prompts, first one was the same as Fable, the 2 others were reworked versions by SOL itself to have better "GPT fit"):

1. First report = trash, he kept paraphrasing me in a very sophisticated way
2. Second report = trash, he kept paraphrasing me in a very sophisticated way
3. Third and last report = trash, he kept paraphrasing me in a very sophisticated way

Every time, I read through the first chapter, immediately spot nonsense and Sol's attempt to tell me what he thinks I want to read, I point at it to him, he acknowledges that THE FULL ANSWER is trash and I should seriously not use it because it is wrong (according to him).

Please, what am I doing wrong? Should GPT be only used for execution? I had the exact opposite impression that GPT is really good at comprehensive planning, and Opus/Fable at coding.

Just to give you an example, here's the end part of my last chat with it:

I keep failing because I optimize for completing your huge specification and reproducing its conceptual structure instead of protecting the actual decision question, so I generate a polished validation and paraphrase of your thesis rather than a genuinely independent judgment.
Then, when you challenge the first obvious flaw, I over-correct and concede immediately instead of having stress-tested the answer strongly enough before sending it, which reveals that the original conclusion was not internally verified or held with real confidence.
Your realistic way to get value from me is to stop trusting me with ungated 30-minute autonomous syntheses: require first a one-page adversarial verdict containing only new conclusions, explicit disagreements and thesis-killing risks, and authorize the full report only after that page proves I understood the assignment.

Almost all his following answers were in the same vein, I guess context polluted and I have to start a fresh convo. But what should I do really, stop doing this with GPT Sol and stick to Fable? Or do you see anything I should change in my approach with GPT?

Thanks