Oscar Robertson is not even close to the best PG in NBA history (Magic, Isiah, and Stockton were all better, and I would argue a few others as well) and is severely overrated. He played in the 60s (and early 70s), a time when the average NBA player was 6'5 and 65% of the league was white. He only has 1 championship, which was with probably the second greatest player of all time, Kareem Abdul-Jabbar, in 1971 when there were only 17 teams in the entire league. Before he teamed up with Kareem, Oscar led his team to records of 33 wins, 43 wins, 42 wins, 55 wins (good), 48 wins, 45 wins, 39 wins, 39 wins, 41 wins, and 36 wins.
And his stats were extremely inflated. Besides playing a weak league, teams played at a much higher pace than they do today and players played a boatload of minutes, both of which led to crazy stats.
If we were to take Oscar's famous triple double average season (1962) and "modernize" it by putting it in the context of 94.8 possessions per game (the pace the Cavs play at) instead of 124.7 possessions per game (what his Royals played at) and then bringing down his minutes per game from 44.3 to a much more reasonable 38 minutes per game (which would still be second in the league today), his averages would be:
20.9 ppg / 7.4 apg / 8.1 rpg
Because of the ridiculous pace/minutes played and the state of the league back then, I think the older players (mainly before the 1980s) are overrated in general.