I'm not sure how to rank the all-time NBA coaches and GMs.
Red had that amazing run as a coach, and if you want to say "well he Russell and all that talent," then you should give him GM cred for not only building those teams (with at least 2 complete lineup restructurings from the Cousy / Ramsey / Sharman days to the Sam / KC / Hondo team, with only Russell and Heinsohn as the main constants), but also the Cowens / JoJo / Hondo team and the Bird/McHale/Parish team and those 5 post-Russell championships. Riley I think has to be mentioned, too, but then there's Popovich who built multiple great teams over a long stretch in a much bigger league (spreading talent thinner). While he had Duncan and a lot of other stars, I don't think he ever had an era-defining guy on his roster like Riley and Red had, sometime in multiples.