It blows my mind that there are still people saying that Chara is a top-3 Bruins defenseman. For a moment, let's totally ignore anything that Orr, Shore, or Bourque did outside of Boston. You'll find that it does very, very little to change any of their legacies. The only things that seem at all significant off the top of my head are Bourque's Cup with the Avs in 2001 and Orr's cant walk but still the best player on the ice performance in the 1976 Canada Cup. Still, their resumes are impeccable even without those "extras." If their careers had ended when they left the Bruins, I don't see any of those big three being viewed any worse than they are.
But just for the sake of argument, let's look at this whole thing, giving an advantage to Chara by allowing his entire career to be considered and the others only having their years in Boston. Chara's resume does gain something because his five all-star selections go to seven including the two he got in Ottawa, which is a 40% increase. Now, we took one away from Bourque, but he had so many it's not really missed. Regardless, this is what we're looking at:
Orr in 10 seasons
3 Hart Trophies (8 top-5 finishes)
8 Norris Trophies (9 top-five finishes)
2 Art Ross Trophies
9 All-Star selections (8 first, 1 second)
Bourque in 20 seasons (I'm not including the half season for the sake of simplicity as well as intentionally giving a slight skew against him to make a point)
5 top-5 Hart finishes (and many believe he should have won one of those)
5 Norris Trophies (13 top-five finishes)
All-time leader in goals, assists, and points by a defenseman
17 All-Star selections (12 first, 5 second)
Shore in 13 seasons (same as Bourque on the partial season, though it means less here)
4 Hart Trophies (8 top-five finishes)
He played before the Norris, but the Hockey News reckoned he would have eight in 2018.
No records or scoring titles, but his offensive style literally can't be overstated for the day he played in. He was Bobby Orr long before Orr was born.
8 All-Star selections (7 first, 1 second) BUT! All-Star selections weren't made in the first few years of Shore's career. I'm going to go uber-conservative and just give him two more first team nods for the two years he finished third in the Hart balloting. The truth is, I'm likely selling him two selections short.
Chara in 22 seasons
Best Hart finish: 8th
1 Norris Trophy (seven top-five finishes [two of which were in Ottawa])
7 All-Star selections (3 first, 4 second [one of each was in Ottawa])
No offensive accolades, though he is known as a stout defender. However, Orr and later Bourque weren't too shabby in their own end either, and I don't think there's anything special enough about Chara's defense to cover the massive offensive gap that exists. And that's even when I try to look at things as favorably to Chara as possible.
Now, it might seem a bit pointless to include Orr's block in this, but I did so for a reason. Taking everything into account, I have no problem saying that Bourque and Shore are closer to Orr than they are to Chara. There's literally no comparison here. Make things more favorable to Chara by allowing his accolades in Ottawa, and he's still lapped by the other three.