Training to your body type has validity and it also has been around for decades. One thing I learned about this title is that regardless of body type, most people are going to train according to their personality and their mindset. I'M a perfect example of not training to match my body type. I tried it, I don't like and it does not feel normal for me.
Let me explain. I ran track in high school, I ran the 220, 440, and 880 at that time and was also good at basketball; very good at, and it came naturally. Football on the other hand did not. I had trouble running with pads on. I have long limbs for my height. According to "training to match body type" power-lifting and its associated training methods would be out of the question, not my body type. The contradiction is; it was perfect for me mentally.
While the strict method of power-lifting advocate's very low reps (1-5) reps most of the time, mentally and physically I responded best in the 6-10 rep range. I also gained greatly by incorporating Olympic style lifts into my training; 6-10 rep range again. Ironically, these lifts would not be the best for my body type.
If you notice the relationship between track and my style of lifting, you could describe the 100 YD dash as the very low rep range and the distances I ran would be that 6-10 rep range. More than that and I get bored and disinterested. I probably would have been better running the mile and over but mentally, it is not me and lifting according to my body type is not me.
Technically, what presumably would be best for my type would be higher reps (8-12 reps) and more toward a bodybuilding method. Psychologically that is not me. With awareness of your body type and knowledge of the sport you are training in, you can identify possible weaknesses while performing certain movements. With the knowledge, you can find those moves that allow you to overcome those weaknesses.
Those moves in this case will be those that suit your body type. The one overriding fact I have learned is that you will never really know what capacity and ability you have until you experiment and find what your body and mind respond best to. A few things to keep in mind before you run out worrying about your body type. "Body Type" is a bit ambiguous.
It should include your metabolism, muscle length, and your joints. These things are all part of "body type". That's why experimenting with what works best and keeping a journal are your best tools to work within your body type.