Thanks for the input, all.

Some quick answers to the questions posed:
I've been a BAEC member for a few years due to prior travels in/out of LHR, so I instinctively used BA for the first trip and realized I could get OW Sapphire in short order by continuing BAEC FFP bookings for a month until I got to the 600 tier point mark.

Avios devaluation is not ideal but I should have enough to cash in another TATL trip with companion if I can ever find availability

Upgrade desires are primarily on Intl flights, unless its a Transcon flight in/out of JFK.

Based on your comments, it seems that it may be wise to switch to AA on calendar year (since I don't think I can reach Plat or EXP by December) and leverage the BA Silver benefits in the interim.