In case you weren't aware, there are many martial arts whose effectiveness is debated. Gasp! For example, take the internal Chinese martial arts - the ones that purport to generate power by some vehicle that isn't muscular force. Or read up on the Shotokai.
Here's the problem: you can find testimonials and even videos of people getting hit or thrown around by various martial arts experts. They say things like, "he hit me so hard I was thrown across the room," or, "he touched my arm and electric pain shot across my body, and I was paralyzed." Sounds great, right? I mean, who wouldn't want to learn to do that to another person?
Now some or all of these so-called experts might really be that good. Maybe they could reproduce those effects with an unwiling partner - say, an attacker who didn't know anything about them. My first karate instructor could cause almost unbearabale pain at any time in me, at least, and I was as skeptical as one gets. But in some cases when the person on the receiving end of those techniques isn't a believer - isn't the expert's student or follower - the techniques don't work, or don't work as well.
I tend to be skeptical of so called internal arts. Anybody who starts talking about using their joints or internal energy to drive a punch or kick is either speaking metaphorically or is full of crap. Movement comes from muscles or gravity, and that's pretty much it. You can get a little extra boost by pre-stretching tendons and ligaments, but the primary movers have to be muscles or gravity.
Now... I could be wrong. Lots of people believe in all kinds of other ways to generate power - go to amazon and check out some books on ba gua or tai chi. The thing is that I'm not going to be convinced by any number of demonstrations of some guy's students getting tossed around like rag dolls.
How could I be convinced? Maybe a breaking demonstration under controlled conditions. Get a tai chi master on one of those "Science of Sports" shows and let him hit a force meter or kick a crash test dummy a few times. Numbers don't lie.
How about a throwing/ grappling art? Well, grappling competitions are a good start. If you can submit a guy who is: a) trying to win a trophy; and b) not your student, I'll be impressed.
I just read a chapter on the Shotokai and Shigeru Egami's techniques. I've seen videos of it. It looks like crap. Internal kung fu styles - pretty much the same thing. If you're trying to hit somebody and words like "silk reeling" are coming out of your mouth, you're trying to stay completely relaxed while you strike, and you think muscular development will make you a worse fighter, you've lost me.
I could be wrong, of course - I'm wrong a lot! And I'll be happy to admit it. As soon as one of those guys uses that technique to break something hard or mangle a scientific instrument in a setting managed by skeptics. Or hits me, I guess, though I'm not a huge fan of that particular method!
I will add a couple of caveats. One: tai chi might be great for health, fitness, peace of mind, oneness with the universe, etc. - I'm not disputing any of that, I'm only saying I doubt it's good for teaching people to hit hard. Two: many people talk about internal practices or softer practices and what they mean is a style of training that emphasizes reading subtle changes in an opponent's body position, using someone's strength against them, etc. That's a completely valid emphasis for training. There's nothing crazy or mystical about that. It's the difference between a person doing half an hour of push hands training versus another one doing half an hour of punching a makiwara. The two are just cultivating different qualities that go into making a good fighter. We could have a discussion about which method is the most efficient way to become a good fighter, but I certainly wouldn't say the guy doing push hands is crazy or wasting time.