Fair enough, but of course, SFO-LHR is only a tiny element of comparison for BA. Things would be different on JFK-LHR (where the primary competitor would be DL/VS but not UA), or indeed GVA-SIN (where the competitors would be AF, LH, TK, and EK) or NCE-CPT (as above). The point is that the competitive scene for BA are essentially AF and LH for global European markets, and U2 and FR for o/d European markets.

In practice, focusing your product on what UA is doing rather than what AF and LH are doing would simply be shooting yourself in the foot, in exactly the same way that you would not expect UA to base their product on what, say, AF are doing, even though they are in direct competition with them on ORD-CDG, but rather on what AA and DL are doing because they are their main competitors. Of course, someone flying ORD-CDG in J might wonder how on earth UA is getting away with food which is quite inferior to AF's but the reality is that UA don't care because their food is holding fine when compared to AA and DL.

And of course, LHR-SFO is precisely a BA route where J is packed to the brim, so precisely not a route where BA would feel a particular need to adapt their product.