You need to know each 'part' well to do it all together.
Currently I've changed to a pinpoint position, jumping with both feet, straight ball toss (opposed to circular) and different racquet take back (or up). I started by picking each part and practising it (without a ball most of the times). First I started to get used to use both feet to keep balance and 'jump'. Then was the ball toss, etc. I used to practise these independently of the others.
Then, when I had the basics of each, I tried them all together in a court. Most of the times I couldn't do them all well, but I was able to know which part was failing, and concentrate on it on the next serve, and repeat, and repeat. I still have problems with doing it all together (about 50% of times), but I gained a good 15-20 mph on my serve by being consistent on this.
I'm pretty sure if I just tried everything from the start I would still be hitting the ball with my frame in a best case scenario or hurt my shoulder in the worst.
(Yeah, I changed pretty much everything in the serve
But to defend the 'whole serve' motion. When I started playing, my coach made us practise each part separatly, the ball toss without the racquet for example, which thrown my rhythm out of the window when I had to do it all together. The ball toss was completly different when done without moving the right arm with a racquet. I had to 're-learn' the toss after that.
Bottom line, if the coach is teaching him the small part correctly (for example, a ball toss while pulling the racquet up) I think its ok, but if he separates it like forcing you to hit the ball with your racquet already on your back, I think this will only cause you to mess up since you won't learn any of the timing involved in the serve.
About your friend, he may be righ tor wrong. If he thinks he should do A, but actually has better serves with B, then B should be used, but if he has the same level serves with A or B, and feels more confortable with A while the pro says B, he should use A, unless there is something wrong with his A
It seems a bit that your friend is trying to advance a bit to fast, not because of wanting to use the waist and hip, but because, as you said, he is taking up tennis, and is already 'defying' his pro so he can do the same as the guys/gals he saw on tv. Just a thought thou
Hope it helps,