The comments here about looking outside the window vs being on instruments I suspect is from non jet flying pilots. I recall a quick survey being done on where people look for rotation and it was 50:50 inside vs outside. HOWEVER, those who do look outside for the initial rotation quickly look back inside to the PFD to see where their initial rotation has come to and adjust according to the degree graduations, as opposed to the FD. Almost all said this is as the gear is unsticking or has just become airborne. So really, most people are rotating on instruments because they quickly look inside to see here they are - particularly important on the 777 with regard to tail scrapes.
The use of the FD for rotation I have to admit is incongruous. It moves to a pre determined and fixed attitude until airborne and so is a waste of time initially. Rotate towards 15degrees, get established in the climb and then start following FD cues WHEN IT CATCHES UP. So the point is - those rotating purely based upon head inside aren’t using the FD, they are using the PFD to rotate to an angle and checking speed, then checking to see what the FD is doing. If there are Boeing jet pilots that are rotating solely on the movement of the FD I’d be very surprised, and to be honest anybody who is is very poorly trained (I’d find it hard to believe they’d been trained) and has rocks in their heads.