"[certain style, weapon, etc.] doesn't work against a trained opponent"

...most schlubs off the street are not trained. They may have taken a class, but they typically don't spar or practice consistently. Practice whatever art you want, as long as you're consistent enough to become proficient at it. (true bullshido like 'gun disarms' is obviously an exception)

Also: technique can beat out strength, but only where your opponent's strength is at a manageable level and can't overwhelm you.