Even with a robo-ump behind the plate, the flesh and bones umpire will still have a huge impact on the game there so the earpiece thing can still work since he's far from a mimic. Safe/out calls at the plate, determining foul tips, hit batsmen, balks etc.
I think people are far overestimating the tendency for umpires to make a mistake. I think they do a pretty damn good job overall and the bulk of them aren't f***ing *******s who dedicated their life to upholding the integrity of the game as best as they can to their ability. It's basically a thankless, though well-paid job, no different than a garbage man or bureaucrat. People will hate you if you mess up once, but not thank you for the other 99 times you do a great job.