It's not a myth, but I think it's often exaggerated.
I think there's definitely a strike-zone "gap" (on the upper side) between the 2hbh and the 1hbh (with the 2hbh being higher).
This gap is huge at the lower recreational level where people are using the wrong grips for the 1hbh and/or don't have the right timing.
As the skill level rises, the gap shrinks but doesn't completely close.
There are always exceptions (weak 2hbhs, strong 1hbhs), but I'm talking about the typical cases.
But what's the reason behind this?
I think the main reason is that to get the racket head high above the shoulders, the 1-hander supinates more before contact. The longer the lag between the beginning of supination and contact, harder it is to time right.
Originally Posted by always_crosscourt
Anyway, try the chin ups, rows and reverse flyes - strengthen the hell out of the upper back and posterior shoulder musculature and let me know how you get on then with high 1hbh's...
What part of the swing does chin ups help with?