And the OP is asking for a personal answer.

They've given most of the specifics you say you need, and demonstrated that they probably understand the subtleties you raise: the downsides of losing flexibility, the need (and implied request) to know more about BAEC.

But the question is whether the bonus overrides these negatives?

I think it's unlikely. An F trip to London would be 170k avios off peak or 200k peak. That's at least 121k MR pre-bonus. Aeroplan would require 140k but that's to most of continental Europe, including stopovers (an add-on would require up to another 40k avios). I also imagine the surcharges through Aeroplan (on a *A carrier) would be much lower, so that route would be much better.