The most effective structure I saw was when the CMO was the strategy lead - her title was Director of Business Planning & Marketing.
Her function included the usual marketing units plus market research, data analyts, and the global business development leads. She put together the business plan with contributions from the other VPs after a three-day workshop retreat to which every manager above team lead level was invited.
(That shared-strategy model would extend, so that all SMT choices would be cascaded down to the individual units, and every member of that unit would feed tactical plans and coalface-level insight back up the chain. The business plan is then an artifact of whole-company discussions. I've taken that model everywhere I've gone since.)
We did bring in external consultants from time to time, and it worked pretty well, but these were tasks where you needed an external perspective - like a brand exercise to bring a few home truths on the gap between how the company saw itself and how others saw it.
The responsibility always remained with the SMT, who had a diligent attitude of professionalism - every senior manager had an MBA (it was a requirement for promotion) and was expected to be highly proficient in strategy skills - I'm genuinely surprised and disappointed if I encounter anyone above team lead level who doesn't have those skills.
There's a culture of anti-intellectualism among tech companies which means that very few do have any kind of business training, and that becomes apparent when they don't understand core concepts like why you need good quality research - "fail fast" has become "just throw out anything and see who bites".
It doesn't need to be formal - for my colleagues, I've recommended that they do what I did (as a minimum) - chain together courses on Coursera that broadly follow the MBA curriculum, starting with the ones from Wharton. If you cover everything, it will still take you up to 2 years to get through something like 40 individual courses, which sounds about right - though, online, you have the option to cram through them faster.
