Hits against aren't the only stat that matters for pitchers. Ryan allows less hits, but gives up more walks. Either way, you put a man on base. When you consider walks and hits, Clemens was responsible for less men on base. They also pitched at the same time for 10 seasons which is more than half of Clemen's career. Clemen's ERA+ is 25% better than Ryan's. Were there nearly twice as many good pitchers before 1984 as there are since 1993? Depending on how someone presents the stats I think you can make a strong case for either of them. If I had to pick one for their entire career, I'd take Ryan since he pitched at such a high level for 7 more years then Clemens. However, if just for one season, I'd take Clemens. I'm probably biased since I saw the Rocket in his prime and Ryan after he passed his best years, but I'd say Clemens was the better pitcher.
or, that clemens pitched in an era where offense jumped off the charts. and really, clemens has pitched, and thrived, in several different eras. consider, his cy young awards are 15 years apart. speaking of postseason hardware, i've seen no one mention it, so i will: clemens has more MVPs than ryan does cy youngs; fairly significant. and lastly, i offer the following, bill james-influenced metrics from baseball reference: black ink: clemens - 91; ryan - 84 measures how often they led their league in wins, earned run average, strikeouts, innings pitched, win-loss percentage, complete games, lowest walks per 9 innings, lowest hits per 9 innings, appearances, starts or shutouts gray ink: clemens - 287; ryan 251 same as above, but measures top 10 finishes in same categories HoF standards: clemens - 68.0; ryan - 55 is used to measure the overall quality of a player's career, ranging from 50 (average HoF'er) to 100 not exact science, but, well, more substantive than "oh, yeah, well..."
ryan's first "year" in the majors consisted of 3 IP and a 15.00 ERA. high level? should we even count that among his 27 seasons? so it's really more like six years, and even that's a little misleading because ryan wasn't a full-time starter until 1972.