Do they use a significant stats component? Absolutely. So would I. But with razor thin margins, attitude, mental makeup, clubhouse culture concerns etc. can make a huge difference.
There's a reason some guys 'can't play in NY or Boston'. Because those intangibles matter. Plenty of guys can't hack it there. Because none of this production happens in a vacuum. And these are human beings naturally ruled by mercurial minds.
I've no idea who's stats are better, but I'd sign Jeter over Machado in an instant, given what I know about the guys (which isn't everything to be sure).