I like the idea you have and the work you are putting in. To backtest a method for MONTHS in past seasons takes a lot of work and patience, so that is something I can absolutely appreciate. I will always contend that if you put the hard work in, you will be rewarded - with the proper knowledge and mindset, of course, which you most likely have with the research you are conducting.
However, at the same time, I will always insist that there will never be a "system" that comes out where you can simply plug in numbers and expect a nice winning percentage, let alone one above 60%. In fact, I think it is nearly impossible to finish a season above 60% (Minimum 300-400 games bet). In my magical season of 2011 over/unders, I could do no wrong, yet still only finished 366-270-42 (57.5%), and quite honestly, that was probably my peak. 60% is pretty much unreal over a full season (Although you can absolutely hit that in a certain portion of the season, but I don't think someone can hit that, with strictly only -110 bets like my over/unders, in one full season), and of course, there is no method or system that can attain it.
I wish you nothing but the best of luck, and I hope you have found something that yields positive results. But overall, I don't think there's any kind of "system" of simply plugging numbers - in any sport - that will command a great winning percentage. If players were robots? Yes, then absolutely. But these professional athletes are no different from you and I; there's way too many variables to try and conduct a system where you just plug in numbers. To me, that just can't work with human beings, especially when we don't see the things that happen off the field (Although this is actually a main reason why I say baseball is the best and easiest sport to bet on because we see them more than in any other sport, and there's less variables for intangible items like that when they rarely get days off for 6-7 months).
The only thing I can advise is this: Look at every game. Every day. Do not take a day off. Your mind will automatically adjust, keeping tabs on every team and every pitcher (Which is what I do for over/unders), while spending countless hours every day over the season studying and just breaking each pitching matchup down. That's the main way to win in baseball, in my opinion. It's hard to fully explain but when you look at everything so long within every day of the season, your mind just adapts and you obtain a true "feel" for the games. It's mental. You gain a knowledge for tendencies, rhythms, streaks, mindsets, etc., and then your mind works from there. Instead of spending a lot of time trying to develop some mathematical system that, in my opinion, will not work significantly because these players are human beings and not methodical robots without variables, try the things I alluded to and you may be better off.
Again, my opinion, but it's a technique that works for me so with you devoting a lot of time like I do, it can certainly work for you as well. Whatever path you decide, I wish you the best of luck and look forward to seeing you on here throughout the season. Good to see you in MLB, by the way, as I remember you throughout football season.