First off you aren't in a court of law, there is no standard of proof required. Nobody's going to jail no matter what, so don't apply some false standard here.
You won't answer the question because you know as well as I do that star pitchers get latitude on balls and strikes less renowned or experienced pitchers do. They get bigger wider strike zones and always have. It's subconcious bias and what motivates as you say is the only thing that's not easy to determine. But its existence is easy to see.. Just like top defensive backs will get away shirt tugs and arm-bars other defenders never would. Remember Deion Sanders arm-barring Michael Irvin in the 1994 Championship Game? That DPI all day long on most DB s but not Deion because he was that good, he got the benefit of the doubt, which is a form of subsconcious bias, Every great DB gets awy with things rookie DBs or less renowned DBs don't? Why because they're the best and thus when they do it they get what they call across the pond "the benefit of the doubt" repeatedly
A more notorious example beyond football would be Christian Laettner stamping on Aminu Timberlake's chest in the 1992 NCAA Regional Final. It was deliberate and normally would or should have led to an automatic ejection but only a technical was given and Laettner ended up hitting the winning shot and that's all people want to remember. Think that if Laettner wasn't an All-American playing for the defending National Champions. Lattner's doesn't get ejected? Again subconscious bias. I could say more on this incident but won't here. Or Michael's Jordan's last winning shot for Chicago on which he got away with one of the most blatant push-offs you'll ever see to create room to shoot.. But all anyone remembers now are those two shots not the actions that preceded and should have prevented them.
Back to your sport baseball. Everyone knows certain star pitchers throughout the history of the game got called strikes on balls outside the strike zone no other pitchers got because the umpires respected their perfomance and excellence and achievements. Again subconcious bias. And don't even get me started on international football or if you choose soccer
Look referees have a tough job, but that doesn't excuse doing it incompetently or inconsistently or based on bias, subconscious or otherwise.. But it also doesn't excuse major league sports from working to make the referee's job as easy as possible, not by eliminating the human element but by making the human element less impactful on the rules their enforcement or the consequences of either.. In fairness that won't help so much at the high school (as far as I have gone coaching basketball), but at the Major League Level absolutely can across all sports. It won't eliminate the human factor at all, nor it will entirely eliminate the potential to minimize officiating's impact on game outcomes immediately, but anything that improves officiating and helps on-field officials officiate more competently, more consistently, and with less room for subconscious biases impacting should be welcome by all fans in all sports.