I'd say I'm only mediocre - I have days where I'm pretty dang competent and competitive and maybe even good, and I've won a few tournament rounds, but I've also come in last on a few and my day-to-day consistency is almost non-existent. But even at home I don't get to play much, I really need to fix that...
...anyway, I will say the whole rulesets thing truly is important. Chuckwurt has alluded to this via several great points.
But few things were as frustratingly illuminating to me as a player, and what would truly be required for tournament play, then the time I was an effing GOD on MET, played for what felt like 20 minutes (and maybe was with people lining up behind me), claimed some xtra balls, made a few few modes, whatever, I had NO IDEA what the rules or modes or anything was... I just aimed for my shots (blinking lights?) and was having a great day of accuracy. Hearing songs, getting multiballs, it was freaking awesome! But of course, it eventually ended.
I don't remember what my final score was. I mean it was good, I thought... but it didn't crack the machine's board. And then I watched the girl behind me, a much better player who was also much more familiar with MET, go three-and-out in like 4 minutes and essentially double my own score. WTF???
Now if I'd stumbled into my god-mode accuracy on an 80's or maybe even a 90's game, I surely would have killed it. But any modern Stern, it seems god mode is not enough: you NEED to know the rules!
This is personally very frustrating to me because there are so many rules even before you add stacks and personalities (characters / houses) and other stuff... so if you're not CONSISTENT enough (which I am not) it can be very difficult to truly explore and appreciate the nuances of a ruleset even casually, let alone competitively.
So yeah, play mechanics are important. They are the foundation of all pinball. You need to start there! But there's a reason everyone wants the kitchen sink and deep rules in the 21st century. Don't discount modern rules: if you're only mediocre, you need to know the rules that best make every shot count.