Please see each airline’s A320 or B737 unless noted otherwise based on seatguru (I did not check all aircraft types). Please correct me if something looks wrong. For layout, the number represents how many seats on each side of the aisle, and 3B means 3 on each side but middle seat blocked

Airline, Seat Pitch, Layout

Clearly Better than BA:
Air Serbia 39 2
Aeroflot 38 2
LOT 37 3B (but B737Max is 34 3B)
Turkish 34 3B
Air France 34 3B
Swiss 34 3B
Aegean 33 3B
KLM 33 3B
Alitalia 32 3B
Croatia 32 3B

Arguably Better than BA:
Austrian 29 1 (Embraer E195)
TAP 32 3 (width 22)

Very Similar to BA:
Finnair 31 3B
Iberia 31 3B
Czech 31 3B (A319)
Lufthansa 30 3B (width 18)
Brussels 30 3B (width 17.5)
British Airways 30 3B (width 17)

Aer Lingus no J
SAS no J

A few comments:

TAP has 3 on each side of the aisle for both J and Y (no middle seat blocked), but seat width shows 22 in J and 18 in Y, is that right? If those numbers are correct, then TAP is better than BA by 2 for pitch and 5 for width, but in return you might have someone sitting next to you if J is quite full.

Austrian has the worst seat pitch, but only 1 seat on each side of the aisle so arguably better than BA.

Finnair, Iberia, and Czech almost the same as BA but 1 better for pitch. Lufthansa and Brussels are equally bad as BA with pitch 30, but seat width is a bit better.

Not sure about carriers outside Europe, but based on this, BA indeed arguably has the worst J seat in the sky, unless other aircraft types would show differences. I could see the argument for BA>TAP for full flights, but that’s about it.