They might be bigger and stronger, but they pitch fewer inning, half of them never have to hit (soon all), and they’re good at fewer pitches. The expectations for pitchers are diminishing.
With all due respect, you are mistaking the minimizing of extraneous requirements in favor of maximizing fundamental talents for diminishing expectations.
True, starting pitchers no longer throw 140-150 pitches/game. Instead, they throw 110 pitches/game -- but virtually all of them are max effort (as opposed to maybe 1/3 of them previously).
True, most pitchers no longer boast arsenals consisting of 5-or-more pitches. Instead, most starting pitchers work with 3 pitches, relievers with only 2. But that is the result of intention to maximize the pitcher's performance. Most pitchers can't effectively command more than three (or two) pitches. The extra pitch(es) too often end up as cripples...and outside the park. Simplifying a pitcher's arsenal usually results in a better pitcher.
True, most pitchers can't hit a lick. Even the better hitting pitchers aren't really good hitters. But that's the result of a century-long trend and a manifestation of the individual pitcher's and his organization's judgment that his primary job is pitching. And working to be a better pitcher will make a greater contribution to the team than working to be a better hitter.
Athletically, pitchers are generally the equal of their position player contemporaries. Realize about 90% of players selected in the amateur draft will be pitchers, shortstops and center fielders -- and invariably the best players on their team. And, as previously noted, pitching is the most physically exhausting job on the field, excepting only the catcher's.
One would be tempted to exclude the likes of Bartolo Colon in any discussion of athleticism. But how many position players will play at 43 next year, like Colon will.