I think there is consistently bad and good practice. Which is essentially a system.
I also don't think you need experience to make a judgement because you can look at progression.
And it is pretty simple. Rokus for example spent years doing one system or method. And then changed that system and got a lot better very quickly.
I don't have to understand Aikido to see that. In fact not understanding Aikido probably helps because all I look for is improvement. Rather than what is ascetically correct.
System, in this case, is a generic term intended to mean any course of training, from a specific school to an entire martial arts style. And if results are being evaluated objectively, it should be pretty easy to diagnose where the anomalies lie. If someone goes to a grappling school and after a year, two years, five years, 10 years, still stinks at grappling, it might be the person, the school, or the entire system that is the problem.
My point is that, if most people who study in a school stink at whatever the school is teaching, it's not the people that are the problem. It's at least the school. But if that school is pretty typical of all of the schools in a style... the disfunction is systemic.
To be very clear, this is simply a comment about people getting good at whatever they think they're being taught. Where this gets tricky is when styles or schools start to bait and switch you by equating two things that are not actually the same. Self defense and something else. Fighting and something else. You might be learning ninjutsu... but are you learning to fight? You might be learning some version of Aikido, but what skills are you actually acquiring that translate to ability outside of the school?
When I hear the statement, "It really is the system," I think that applies to any style that relies on exceptional natural ability in order to excel. In BJJ, MMA, boxing, wrestling, Judo, etc, the beauty is that normal, average, every day people get really good all the time. People who are strong and not strong. People who are flexible and not flexible. People who have never been called 'athletic' in their lives. I mean, sure you can point to the elite athlete and say, "That guy is exceptional." But to demonstrate that the system is sound, and that the training can consistently and reliably build expertise, you can pick pretty much anyone who trains in the style.