I've heard/read the arguments and they rank up there with the same arguments in golf... that today's golf balls go too far.
These arguments are constructed with little forethought into just how the physics of swinging a bat, or a golf club, have become so scientific that both sports are now being overwhelmed with scientific data that relates to bat/club speed and launch angle.
Teach golfers how to maximize their swing speed, be it via athleticism, launch angle, setup, etc. and compare that to how baseball players are now being instructed and taught to swing in similar manners - to achieve those same optimum conditions - you're gonna get the traditionalists in both sports running to the mountains and screaming that the sky is falling.
Much ado about nothing. The quality of our athletes today are much better, their training and instruction is so much better, and their athleticism is so much better than in days gone by.
Maybe there's more of an argument in golf, because of the technology aspect and how it relates to oversized clubs and less-spinning balls.. but still - the Dustin Johnson's of golf would still be outdriving the Jack Nicklaus's back in the 70's. And, quite frankly, I'm not sure that given the power and athleticism of these players today - that DJ couldn't swing at 85% of his usual power and still maintain control and enjoy an enormous advantage.
Throw in shorter ballpark porches, the change in temperatures and climate over the years, etc... it's just difficult to appreciate the complaining pitchers' arguments imo.