Gretzky and Lemieux killed penalties it wasn't really a testament to their strong defensive abilities now was it. Not saying Orr was terrible defensively, but the example doesn't mean a whole lot.
You're comparing forwards to defencemen now. Not exactly apples to apples.
The comparison was Orr and Byfuglien. Byfuglien is very good skating forward with the puck. He's a very impressive puck rusher and is a force on the power play. But without the puck...well, his coach considers him the worst penalty killing option among his six defencemen. And it's not like the Thrashers are loaded with great penalty killers, their PK unit is third worst in the league this year. He still has a lot to figure out about the defensive side of the game. If Scotty Bowman calls him a rover, I'm not going to argue.
Orr excelled in absolutely every situation, whether skating forward with the puck or skating backward without the puck.
His statistics back that up.
Top 10 defencemen in even strength goals for, 1968-75
Among the big minute defencemen of his era (as defined by top-10 in ESGF), Bobby Orr had fewer even strength goals against per game while on the ice than everyone but Serge Savard. So his great offensive numbers weren't coming at the expense of his defensive play. Call him a rover if you like, but he was a defenceman at the same time.
And on the penalty kill, Orr was probably the best penalty killing defenceman of his era, maybe the best ever.
Top penalty killing defencemen, 1968-75
PK% is the approximate % of the team's penalty kill that the player played, estimated using on-ice goals against. TmPK+ is a measure of the strength of the penalty kill that the player played on, where 1.00 is average and lower is better.
Orr played on the penalty kill as much as elite defensive defencemen like Jacques Laperriere, Bill White, and Tim Horton. And Boston had the best penalty kill in the league over this time, allowing goals at 75% of league average. That's an incredible record, and there aren't any rovers on the penalty kill.
Suggesting that Orr was a rover along the lines of Byfuglien is simply uninformed and incorrect.