Some players adjust and some don't.
Howard's career was impacted by his knee injury, but also b/c he never really got comfortable hitting the ball the other way, when he was at his best he would power the ball to left center, but he fell into the pull heavy trap. Maybe because as his power slowly declined he felt he needed to pull to hit HRs? Maybe because it was a habit?
Thome wasn't more talented than Howard, but he was a more disciplined hitter and aged very well.
A good example are hitters who chase breaking balls - a lot of ML hitters can't handle a good slider, but the smarter hitters (those who either can pick up spin or study pitchers for "tells") learn to spit on them, b/c most pitchers struggle to throw them for strikes (and when they elevate them, are more likely to hang them). And the difference between a 2-1 and 1-2 count is pretty substantial in terms of hitting success.
They've worked with Castellanos, but he's said he's not comfortable "thinking" at the plate and is better when he just goes up and hacks away. However, watching him, he's better when he lays off the low outside breaking ball, which every pitcher now tries to get him to bite on, and waits for a pitch over the plate. It's not about trying to draw walks, it's about not giving pitchers "cheap" strikes so he has to make perfect pitches and hopefully makes a mistake.
My point isn't about players being lazy, but Dombrowski putting more emphasis on players who are willing and able to refine their craft. Some players can't or won't, Juan Samuel never hit as good as his rookie season as pitchers learned never to throw him strikes. What is interesting is it seems they do take this into account when drafting/signing prospects, they've add more hitters with good eyes the last couple years.
Yes, you can do this, because opposing hitters do this to our pitchers all the time.
Of course there's Manny Sanguillen, the greatest pure hitter who ever lived, b/c he could literally hit anything, including pitches over his head.
