Like you mention, that's only been a trend in the last 25 years or so. Prior to that, there was some pride is in being a 30/30, 20/50, 40/20, 50/20 and more rarely, a 40/40 player. All of which could get one easily recognized as an MVP. Furthermore, the trend to long ball vs. small ball is that long ball is seen as offensive strategy that has no defense. And I think McGwire and especially Bonds, Sosa had a lot to do with it. Bonds and Sosa came up as solid candidates for 30/30 seasons. Bonds did do a few seasons of 20/50 before he almost entire switched to long ball. And when you could have players that could guarantee a homerun every 10-20 ABs, it's easy to see why long ball is seen as feasible. What's sad that Bonds was an incredibly talented hitter before he went down his long ball route. I mean, he still hit for a high average, slugging percentage, and OBP. But he used to be able to hit the situation, go the other way to avoid a double situation, and he always had an eye for walks. What was incredible to watch was that he overnight (at least it felt that way) cause teams to simply intentionally walk him 50% of the time.
In the 40s-60s and into the 70s maybe, hitters were more balanced. I think of sluggers like Williams, Mays, Mantle, Yaz, Kilebrew, Foster, McCovey, Kingman, etc. The introduction of the forkball, splitter, and changeup in the late 70s and 80s had a lot to do with the down turn in power. Hitter's technologically behind so to speak. In today's baseball, there's almost no room for a more balanced hitter like Gwynn, Boggs, Rose, Carew. Guys who only got 50-60 RBIs, a dozen or two homeruns, stole 15 bases, but who could bat for .350 in a given year and over 200 hits.
It used to be taught, speed has no off days. That doesn't seem to be true anymore.