Ugh, I just feel like you are completely missing the whole point.
You say the sound guy staying the same isn't going to change the game, yet some new programmers, concept artists, motion capturers, character and environment modelers WILL change the game's development outcome? All those people do, is make what is requested of them, from a higher up. Who is the higher up? Boon. The main constant throughout the entire series. They aren't idea men, they aren't going to decide the game's direction, what is focused on, and what type of crowd it is aiming for. Boon and the veterans that have been there for multiple games are the ones who direct the new blood.
Then you go on to bring up Square Enix. How they've changed the head guy, and now the company is no longer the same. That it's not as good anymore. If the lead guy makes that much of a difference, that just further backs up my point. That the head of the MK team, NRS, has remained the same from start til now, and yet the series had highs, lows, and now is better than ever, ever since being given the opportunity by WB. Same head guy, same guys that made the previous ones(more than just the sound guy, all the artists, modelers, programmers etc. are all the same, with a few more people added to make the work load easier).
You just aren't getting it. Sure, MK 1 had what...8 people working on it? Well, MK 2 had double. MK 3 had even more. MK 4...probably 40 or so. MK

A, over 60. They've always added a few more people. The series got worse when they went to a 3D fighting plane. The series got better when it went back to 2D. By MK:A-MKvsDC, they probably had 70-80 people working there. Ok, so MK9 comes around, I bet they added another 10. You really think those 10 overruled the head guy, and the 60+ people that have been working there for years, and completely changed the game's quality from mediocre to great? Seriously?
You act as if they went from 8 people working on MK1-MKvsDC, to 80 working on MK9.