Showdown is easy if you actually play it all the way through.
I’m not a great player by any means, and I’ve completed the 1st inning, AL Central, NL Central, and AL West twice. Some pre patch, some post-patch. As long as you think about what you need for the upcoming moment and organize your lineup accordingly, it really isn’t hard. Put Edwin Encarnacion at shortstop for boss battles, Mitch Haniger at catcher, etc.
Actually take advantage of your perks too. If you get a contact/exit velo boost on the first pitch, swing if it’s anywhere close. Stuff like that.
Obviously if you’re skipping to the final boss immediately, you’re going to have trouble.