leetch and housley each had one career season that topped bourque's in offensive production (housley edges him by one point). but bourque has the better 2nd, 3rd, and 4th best offensive season, based solely on points (all in the 90s).
90 point seasons by defensemen:
coffey - 7
orr - 6
bourque - 4
potvin - 3
macinnis - 2
housley - 1
leetch - 1
suter - 1
the other thing about bourque is he is, along with arguably macinnis, the best powerplay defenseman i have seen in my lifetime. no one kept the puck in the zone or moved it on the PP like bourque did. keeping the puck alive on the PP doesn't necessarily always show up on the scoresheet, but i do consider it a vital offensive skill for a d-man. also, his heavy wrist shot and his ability to get it off quickly and get it on net was second only to macinnis' point shot in his era.
at even strength, bourque didn't rush it like leetch or coffey did, but who had the best outlet passes of the last 30 years? bourque and lidstrom. they weren't always, or even very often, long bombs that resulted in breakaways, but they were almost always the safe play (you almost never saw these guys sending up suicide passes), and usually left their recipients in good position to engage the offense.
as you said, bourque played ridiculous minutes and had to conserve his energy. you watch pronger in last year's playoffs and how he moved as little as possible and played with such economy so he could be on the ice for 30 minutes a game. that was bourque's entire career. and, to my eyes at least, his outlet passing was at least as effective as rushing the puck up ice himself, and had the added benefit of helping him stay in position in case the play came back the other way.