A few things to remember:

You can only earn status on BA EC by buying the more (economy) expensive fares that earn you tier points. Cheap (economy) fares don't earn any point. If you fly paid BC/FC, it doesn't matter and is to your advantage (you qualify much faster).

BA awards are relative expensive. e.g., 80,000 mies for trans-Atlantic in the back, and multiplier of 2x and 3x for BC and FC (IIRC). However, 1 CoS r/t mileage UGs are only 0.5x so WT+ (econ dlx) to BC U/G is only 40k miles r/t.

Award inventory availability is reportedly best for the home airline so CX flights are easier to get using CX AMs than BA EC and v-v.

AMs expire some 3 years after you earn them. Can be extended for a fee though. You can also get a AM affnity credit card in Canada.

AM used to be BA's programme for those domiciled in Asia a few years ago so BA award inventory availability may still be good. Upgrade awards on BA may also be available. Not 100% certain.