You are right about so-called 'freebies' at BA. Premium means just that.

Flying full-Y you'll get decent miles. Discounted-Y will not get anything like as healthy a mileage posting as you would on UA, and the mileage bonus you'll have been used to as 1K/1P on UA..... well, forget about it with BAEC Silver!

As already noted though, BAEC Silver is not at all bad - head-and-shoulders better than *A Silver.

Couldn't comment on comparison with AA. I've never flown with them!