I have the defensemen ranked like this
Robinson
Park
Chelios
Coffey
Coffey sucked in his own end, while Chelios was a strong 2 way defender and a very physical ( at times dirty) player. As a 46 year old on a cup winning team, Chelios was still getting a tick under 17 minutes a game in the regular season and just under 13 in the playoffs. When Coffey went to the Flyers, during the 1996-97 season, He was so bad defensively, he played forward on the 4th line and defense on the 2nd PP unit.
Why Park over Chelios? I realize Park lost 4 Norrises to Orr, but other than Orr, the guys Park beat out was a fairly weak group. In other words, Orr and Park were both great, but other than them, the competition among early 1970s defensemen was quite weak (it got way stronger in the late 70s as guys like Robinson, Park, and Salming came of age).
Meanwhile, Chelios peaked at probably the toughest time ever for defensemen:
(FOLLOWING IS A REPOST FROM HOH TOP DEFENSEMEN PROJECT)
I'm fairly confident in saying that but for Bobby Orr, Brad Park would have 4 Norrises... and they'd be 4 of the weakest Norrises of all-time, with MUCH weaker competition than Lidstrom faced on average.
Compare to Chelios who actually did beat out prime Ray Bourque (and Al MacInnis and Paul Coffey) for 3 Norrises, the first two in convincing fashion. Here are the years when Chelios finished top 5 in Norris voting - talk about competition!
1988-89: Chris Chelios, Mtl 226 (37-12-5); Paul Coffey, Pit 115 (14-14-3); Al MacInnis, Cgy 57 (3-10-12); Ray Bourque, Bos 56 (3-8-17); Steve Duchesne, LA 30 (2-5-5)
1990-91: Ray Bourque 257 (35-27-1); Al MacInnis 228 (27-28-9); Chris Chelios 56 (2-9-19); Brian Leetch 30 (2-0-20); Paul Coffey 8 (0-0-8)
1992-93: Chris Chelios 201 (33-10-6); Ray Bourque 97 (6-19-10); Larry Murphy 93 (9-11-15); Kevin Hatcher 17 (0-5-2); Phil Housley 16 (1-2-5)
1994-95: Paul Coffey 69 (12-3-0); Chris Chelios 39 (2-9-2); Ray Bourque 20 (1-1-12); Larry Murphy 7 (0-2-3) (weird voting with the lockout)
1995-96: Chris Chelios 408 (22-19-9-3-1); Ray Bourque 403 (23-16-8-7-0); Brian Leetch 245 (6-6-23-7-7); Vladimir Konstantinov 131 (2-6-7-10-4); Paul Coffey 83 (0-4-2-12-9)
1996-97: Brian Leetch 494 (42-8-3-1-0); Vladimir Konstantinov 178 (2-10-13-6-5); Sandis Ozolinsh 176 (2-12-9-8-3); Chris Chelios 172 (0-7-18-9-6); Scott Stevens 171 (7-8-4-7-4)
2001-02: Nicklas Lidstrom, Det 472 (29-20-7-2-1); Chris Chelios, Det 431 (28-10-13-4-4); Rob Blake, Col 321 (4-19-22-12-2); Sergei Gonchar, Was 147 (0-6-6-22-9); Chris Pronger, StL 62 (0-4-1-8-5)
Note also that Chelios, as a defense-first defenseman (especially in later years) was at a disadvantage, as postexpansion voters often look to stats first.