Yep, SK Thaz gear is better tank gear because they are meant to be better tanks. Paladin stuff is geared more towards their melee DPS role.
By this logic, the proc on the pally bp is more of a statement of:
The bp proc only helps if the paladin is tanking.
Thus making the proc pretty useless to say the least. Its like, "when your tanking, we'll give you more dps, although we'll rob you of a buff slot while doing so. Although, you probably would rather have another buff in that slot to tank better with when you surely are tanking."
In sum of the bp proc:
Its one of those things you don't need (and I personally do not want) when I do have the ability to obtain it. Its more detrimental than beneficial.
I would honestly rather have no proc than that proc. I strongly support changing the proc, taking it off and replacing it with some other stat/focus effect, or even just taking it off.
To be fair regarding the sk vs pally legs; the sk legs definatly have a large dps improvement aswell (affliction enhancement 6).
As a whole though, the thaz items have been done very well, especially if you consider the sets as a whole.