What did Howe do to not make it in the top 10? Otherwize I agree with your notion about Lemieux.
Howe was an NHL captain for what? A couple of unsuccessful years? Sid Abel, Ted Lindsay, and Alex Delvecchio were all longer serving captains.
I would definitely have Sid Abel on the greatest captains list. Here is my attempt:
1) Jean Beliveau
2) Mark Messier
3) Bobby Clarke
4) Sid Abel
5) Denis Potvin
5) Scott Stevens
6) Steve Yzerman
7) George Armstrong
8) Dit Clapper
9) Joe Sakic
10) Bill Cook
11) Emile "Butch" Bouchard
12) Syl Apps
13) Wayne Gretzky
14) Milt Schmidt
15) Dave Keon
16) Ted Kennedy
17) Toe Blake
18) Ted Lindsay
After that I can't make up my mind, but the following are all options in no particular order:
Alex Delvecchio
Dirk Graham
Ron Francis
Rod Brind'amour
Sylvio Mantha
Babe Seibert
Guy Carbonneau
Newsy Lalonde
Doug Gilmour
Jarome Iginla
Art Coulter
Mario Lemieux
Shane Doan
Nicklas Lidstrom
Henri Richard
Maurice Richard and Yvon Cournoyer were each captains of dynasties, but strangely there isn't much written on their leadership abilities.
I only included NHL captains, otherwise Boris Mikhailov would have a good shot at the top 10.