I think people need to keep in mind that baseball is a sport where you can fail 70% of the time at the plate and be one of the best players. It might feel like you're doing shitty, but you're probably doing alright. Like the guy complaining about all the double plays he hits into, but then states his amazing win/loss record.
Also if you're actually sucking then don't feel bad for dropping the difficulty down, especially if you're not the type of person who sticks with games for a long time. If you're gonna get 20-40 hours out of this over the next couple weeks and never play again, drop it to rookie and pretend you're a baseball god instead of cursing at the screen.
If you do want to get good at hitting, your first step is to not swing at at the first pitch. And then condition yourself to only swinging at pitches you can actually drive, just because it looks like a strike doesn't mean you should swing.
Approach each at bat like a hitter would IRL. At the start of each at bat you should have some sort of goal, sometimes it's as simple as not hitting a ground ball. If there is 1 out and a guy on 1st, your main goal is to move the guy over to 2nd, to accomplish this you need to avoid hitting a ground ball at all costs, therefore you tell yourself not to swing at anything low or off-speed, even if that means getting a pop fly or striking out. A real coach would see that you're doing your best to avoid a double play and move the runner over. You coach would be furious if you hit into a double play by swinging at a low change up and still had pitches to work with.
These are some the intricacies of baseball that I love, and I think why so many baseball fans love The Show, however people with out a deep understanding of the game suffer. In games like Madden, anyone good at video games can figure out which plays work and be pretty good at the game with out knowing much about football. With The Show, if you can't figure out that swinging at the first pitch is a bad idea, then you're destined to not be very good.
