ByeByePoly
G.O.A.T.
I'm not saying Pros don't get big shoulder turn or they don't have the shld/hip separation because they often do. What I'm saying is that pros hit big power off many different incoming balls and they will vary the turn to suit their intent and the type of ball they receive. Shoulders and hips are more an issue of amplitude and need to be seen as a variable, not a given. Constant focus on the shoulder turn can tend to lead to snatching the racket from the slot, which will spoil the swing. Imo the key is to focus on proper racket accel technique. The real unit turn is coming out of the slot imo. The hips are driving the shoulders, arm and hand as a unit, dragging the racket to find alignment towards contact. Once great alignment and timing is assured as the hand nears the ball, then the hand starts to tighten the arc, leaving the unit and moving strongly across the body midline instead of continuing in the shoulder plane. This move coincides with the big accel we see right before contact and is the major key to consistent big shots.
Yes this is an outlying exaggeration to make a point, but here we can see with a faster incoming ball, Blake hits a screaming big Fh with limited hip and shoulder turn. I realize this isn't typical, but it still illustrates my point at the extreme edge. He adjust his coil amount to suit the incoming speed of the ball. This is part of why we see most players struggle against big serves...because they feel they need big shoulder turn. Imo, if players learn to modulate or adjust shoulder turn routinely based on the situation, then the adjustments for serves and receiving big Fhs will be much more intuitive and natural. The constant focus a big oversized turn is Imo quite unnecessary and will happen naturally or with mild input if this is taught properly from the start.
"I haven't seen a pro hitting big pace FHs on neutral balls"
There are so many variables in tennis, it's hard to generalized technique. But what I mean by "neutral" above is "neutral baseline shot where you have to generate your own pace". Not talking about serve return, and not talking about concessions one makes at the baseline when rushed. Also... I would agree there are variations of pro shots from the baseline, and perhaps even on "neutral" balls where the shoulder turn is varied. But in general, IMO ... if a pro is trying to hit pace off a neutral ball, they will have full shoulder turn past the hip in the backswing (before the slot).
You will have to explain more what you mean by "snatching the racquet from the slot". I just see the shoulder turn prior to butt cap forward is required prep on neutral balls. Some of this might be stance related. I mostly look at video of Fed (and others) hitting off baseline FHs off the back leg in semi open stance. I haven't paid to much attention to i/o FHs from his backhand corner, but there is definitely different stance dynamics going on from those shots (load bearing on left leg/foot).