As pointed out above, BA does not equal AA when it come to redemption.
For example - on a travel from NA to Europe, BA has 3 zones in Europe, each costing different amount of miles; with AA it's all the same.
Also, if you get a J reward on BA from SA to NA, you will travel J only to your NA entry point (MIA, NYC); if you need to go to ORD or DTW, etc, it will be in Y as there is only Y or F and BA will give you only Y for the domestic segment (unlike with AA where it would be in F domestically).
There are many other differences as well - usually (but not always) worse than AA.