You're describing a problem that mostly doesn't exist - at least not if you're working in performance marketing rather than some ivory-tower "strategy" role.
Seven years in paid search taught me that the best strategic thinking comes from running campaigns, analysing data, and seeing what actually moves revenue. That stuff is documented daily in your ad accounts, your analytics, your client reports. It's not some sacred secret guarded by NDAs. Most strategic "secrets" are just variations of: test more, understand your attribution, and don't be afraid to kill what isn't working.
If you can't find marketing strategy SOPs, it's because the people writing them are either (a) running the same generic bullshit as everyone else, or (b) hoarding mediocre ideas under the illusion of exclusivity. AI trained on that will give you back the same middling advice, sure. But if you feed it your actual data - conversion paths, LTV by segment, channel-level incrementality - it can surface patterns that most "strategists" miss.
The real problem isn't AI's quality. It's that most people claiming to do strategy are just rehashing 2008-era frameworks wrapped in LinkedIn buzzwords. Start with what actually works in your account. That's your real SOP.