Weight training is far from useless.
The key is you have to clearly define your goals.
I actually bought Matt Furey's book a few years ago, and did get great results from what he calls his "Royal Court" exercises. Hey, they are indeed great exercises.
Bodyweight exercises are good for developing relative strength (i.e. being strong compared to others of similar size) and mucular endurance, but there are different types of strength that require external resistance (i.e. weights) to develop. For instance to develop maximal absolute strength, you would have to do lifts with heavy weight (low reps, 2 to 4).
Most athletes have a periodized approach to there training. Here is an example of how it might look for a martial artist:
- General physical preparedness -- emphasis on bodyweight exercises to increase relative strength; also core and stability exercises
- Lift moderately heavy weights (Approx. 70% of the 1RM or 3RM -- one rep maximum or theree rep maximum. This is the amount of weight the trainee can lift with good form one to three times successfully) to stimulate bulk/lean muscle development (hypertrophy). This will generally include bodybuilding protocols. Here is what most people identify as weight training and if you stay here for too long, it may have a negative effect on your martial arts training. You may become too big, too slow, and lose flexibility.
- Lift heavy weights to deveop absolute strength. Here you lift 90% to 95% of your 1RM or 3RM. Here the reps are kept very low. Examples of the lifts to do would be the the deadlift, squat, chest press, and the side press. Certain bodyweight exercises like pistols, one-arm push ups, handstand pushups, and one-arm chinups also develop brute-like strength.
- Develop power/speed/rate of force by doing quick lifts with light weight (30% of the 1RM or 3RM). Examples would be the snatch, dumbbell swings, clean and press. Plyometric exercises would also be included here. I'm talking about exercises like medicine ball throws, box jumps and such.
It is important to take adequate rest periods between sets. Please do your own research to learn more about how much rest should be taken between sets. It will depend on the attribute your trying to develop and how much weight you're working with.
Here are some good places to start:
www.mikemahler.com
www.dragondoor.com
www.workingclassfitness.com
Remember first and foremost that your are a martial athlete and dojo/dojang/kwoon time takes priority over the gym. That is to say skills refinement takes priority of weight training or other exercise.
Mix it up and keep it interesting. Variety is the spice of life. Besides, if you do the same thing over and over again, you subject yourself to negative returns on your investment and overuse injuries.
Peace & blessings,