I try to take a multi-faceted approach considering peak, prime, longevity, playoffs, defense, quality of teammates. For whatever it's worth, I have Kurri at 25 all-time. If you want to isolate to a 20 year period around his prime (1975-1995), I would have him 4th behind Makarov, Lafleur, and Bossy.
Richard way above Kurri is pretty easy. Richard's goalscoring prowess was phenomenal and is still probably the best playoff goalscorer ever.
These four players are all an interesting comparison. They all won multiple Cups on deep teams and usually played with an all-time great centre(Richard with Beliveau, Geoffrion with Beliveau and Richard, Bossy with Trottier, Kurri with Gretzky). Everyone except Kurri had at least one season away from that centre or when they greatly outscored that centre (Richard 1945 (though he played with Lach), Richard 1951, Richard 1953, Geoffrion 1961, Bossy 1986). All were strong playoff performers, though I do think Richard and Bossy were good enough that it becomes a clear advantage. All were better goal scorers than playmakers. Kurri is the clear best defensively though.
If you want to compare their offensive resumes. Some of Richard's resume is war-effected.
Points
Richard: 2, 2, 2, 2, 2, 3, 3, 4, 5, 6, 8
Geoffrion: 1, 1, 4, 6, 6, 7, 7
Bossy: 2, 4, 4, 4, 5, 5, 6 6
Kurri: 2, 2, 4, 7, 8, 10
Goals
Richard: 1, 1, 1, 1, 2, 2, 3, 3, 3, 4, 4, 5
Geoffrion: 1, 1, 3, 3, 5, 5, 8
Bossy: 1, 1, 2, 2, 3, 3, 3, 5, 7
Kurri: 1, 2, 3, 5
Kurri is hurt in that after 1988-89 he puts up good but not great season. He showed he could produce at an elite level away from Gretzky, but not consistently and certainly at a spot where he could be a top scorer over a whole season away from Gretzky.