Just for giggles, I'm going to give you the stats of 2 pitchers... one is in the Hall of Fame and generally regarded by sportswriters as one of the best pitchers of all time. The other is not in the Hall of Fame.
Player A: 324-292 overall record (.524 winning %), 3.19 ERA (3.57 was the League ERA over the same time period), 112 ERA+, 1.25 WHIP, 5714 K in 5386 IP, 2.04 K/BB ratio, 3.07 postseason ERA
Player B: 287-50 overall record (.534 winning %), 3.31 ERA (3.90 was the League ERA over the same time period), 118 ERA+, 1.20 WHIP, 3701 K in 4970 IP, 2.80 K/BB ratio, 2.47 postseason ERA
As you probably guessed, Player B was Bert Blyleven, who is still not in the HOF. Player A is Nolan Ryan, certainly an excellent pitcher, but also one of the most overrated pitchers of all-time.
If you look closely, I'm not sure Ryan is a better pitcher than Blyleven. When Ryan was on, he was great (strikeout record, 9 no-hitters), but he also has thrown more BB than anyone else ever. Ryan has the lower raw ERA, but he did it in a time where ERAs were generally lower, which results in a better ERA+ (ERA in relation to the League with 100 as the average) for Blyleven.
In the end, Nolan Ryan was the better strikeout pitcher and gave up less HRs than Blyleven, while Blyleven had much better control while still maintaining good strikeout dominance (higher K/BB ratio than Ryan. Both were very dominant when they were on their game... Ryan had 61 career shutouts, Blyleven had 60.
But there should be no need for this discussion. Both guys belong in the Hall. So how is Bert Blyleven, one of the top 20 or 30 pitchers EVER not in the Hall of Fame yet? Your guess is as good as mine. Bottom line, Bert Belongs.