Russell played with better bigs than Rodman therefore he has less chance to haul in a larger percentage. So of course, Rodman will have a higher percentage of team rebounds because aside from Pippen his bigs sucked at rebounding. These are career averages.
Hiensohn at 8.8 ( 5.9 adjusted to present time possessions per game)RPG smokes Luke Longley's 4.9 ( 7 adjusted to 1960 possesions per game). Both Pippen and Jordan were good rebounders for their positions 6.2 (8.9) RPG for Jordan and 7.6 (10.9) RPG for Pippen. But a lot of Celtics were this good rebounders from their era, Havlicek was 6.3 (4.2) RPG, Sanders was 9.4 6.3 adjusted) RPG, Sam Jones 6.4 (4.3) RPG, Cousy was 5.2 (3.5) RPG. In fact, both teams were awesome team rebounders. But Bigs have an decided advantage at rebounding as they are closer to ball more often than not. Rodman's other bigs during the Bulls era were duds aside from Pippen. You can't say that of Russell who had competent rebounders all around him. Its far easier to compile stats when others around you can't perform.
All Rodman had to do was rebound and defend one big. He wasn't the center of the team defense that Bill Russell had to be all the time. Rodman was great, I don't argue that, but I think many simply discount the past.