Indeed. I have some similar examples. I collect with BA, even though my primary is AA, because I routinely find some situations where BA makes more sense than any US based airline (and I'm based in the US):

At Avis you earn 500 BA miles for any rental (tho you have to use their AWD so it won't work with corporate rentals that require a different AWD, but my rentals are paid on my own dime). All us airlines earn a piddly 50 miles per day, except when bonuses multiple that (but much of the time bonuses require jumping to off-airport car rentals which take way longer, and still don't add up to 500 miles for a one-to-three-day compact rental).

At Candlewood Suites (part of the Priority Club hotel chain), you earn a whopping 1 mile per $ spent, and one-night rates are often <$100, and thus <100 miles, with all US based airlines (except Southwest). But BA offers a flat 500 miles per stay at these hotels! It seems obvious to me (given that I already collect with BA).

... Except I also collect with NW. And so for a few months right now, they make more sense than BA for these same hotel stays, because NW's Perkology promo is giiving me 1000 bonus miles on top of whatever I earn at the hotel, for any length/cost stay!

But I never collect with BA or NW unless it's a difference like this. (But since neither of them expire as long as you have activity, I don't care that I'm increasing my balance there only gradually.)

However, I would watch out for expiration policies: Other than BA and a cojuple others, it seems most European and Asian airlines have "hard" expiration policiies, meaning miles expire after a few years with no "activity" exception. With "hard" expirations, I would be hesitant to accumulate miles slowly (only when the bonuses are good), because there'd be too much risk of never redeeming them before they expire.