"Ski Slope" isn't thought of as a truss rod problem, since the rod has the most effect from the nut to the 7th fret or so, but early Music Man literature boasts of a new improved truss rod design, that IIRC attemps to prevent this.
By the way, I'm not trying to impugn Fender basses in any way. I'm a huge fan of them and own 4 original '60s Jazz Basses, a sunburst slab board 1962 I've owned since 1993, a sunburst 1964 I've owned since '81, and Candy Apple Red and Olympic White '65s. Since 1974, I've owned more Fender basses than I can count. I like Gibsons and Rics as well, but at the end of the day There Are Fender Basses And There Are Other Basses...
However, I do know that '50s and '60s Fenders are far superior to ones from the late '60s on. I've just seen too many bad '70s Fenders and too many incredible Pre-CBS ones to not know that to be the truth. There are exceptions but in general, that has been my experience.