slominer,
“Some of the major Jewish singers today have a song of “shelo asani goy”. If they came out with a song of “shelo asani isha” would that be any different/same or more or less offensive (or no different) than singing shelo asani goy?”
It would be offensive.
“And, more importantly, why – given that they’re both brochos?”
Nothing to do with the fact that both are brachos, and everything to do with the motivations of the songwriters and singers.