2 seam, 4 seam and 2 types of cutters (vertical and horizontal lets say for those who do not understand) are all thrown the same. Same mechanics, same velocity. The only difference is the end result of the movement and placement. There are 2 cutters that should vary 2-3 mph off from the others solely because of "drag", not because of different velocity or mechanics.
Listen, I agree that every player is different in many ways. The build and makeup being the biggest difference. However, with that said, mechanics are the same overall except for those who have good results with a terrible mechanical delivery. Those are few and far between and do NOT have a very long career. YES, pitching overhand is NOT natural for the human body. It is what we are willing to accept to play the game as we know it though. Intelligent, proper off season with a good in season program, combined with the commitment to be mechanically sound will help with this unnatural motion as much as possible.
I have 2 sons. One throws from each side. My oldest is in the upper 80's with one year to go, my youngest is in the low 80's with 3 years to go. I have played and coached for many years. I have made it a point to be informed and involved in today's science. Here's my last info on this matter:
Do NOT be in a hurry for your kid to be a standout at the cost of his arm just because you are NOT informed and rely and trust some guys who are coaches or instructors. Not everyone involved in the game knows very much about the game. Yes, and I may get cussed at for this but, there are D1 programs out there that have terrible pitching coaches/philosophy and it is apparent when you dig into their programs. (look to see about past player injuries, transfers, etc to see how they do NOT retain a pitching staff). Teach your kids sound fundamentals/mechanics first before anything. FBs only until they are 10/11. Then work in a circle or 3 finger change for off speed. These are not hard on the arm whatsoever. At 14/15, you should start the "concept" of a curve in practice without throwing it full bullpen. Small drills working on grip and rotation only. At 17, you should have developed a full curve and use it very very sparingly in your last HS year into your senior summer. Do NOT throw long toss beyond 120'. Make sure you have a running program implemented into your training and focus on pylometric training that is meant for the specific position of pitching. Mechanics always to keep bad habits from forming when in the middle to end of your season and the ability to say NO to a coach who often sits on a bucket and calls signs that results in deception pitches that will end your velocity (aka velocity) before you get going. Most of the guys on the buckets have never pitched before and have some old school mentality that a curve is the only "out" pitch a pitcher has. That is sooooo NOT true.
On and btw, most MLB guys will quickly tell you that when they introduce a slider into their arsenal, their velocity decreases quickly. Just fyi. Many do NOt throw it and are very effective.
Good luck to all......For Love of the Game~