Stinger, I went from a TH-57 to a Huey to an SH-2F.
What people do nowadays is go from the TH-57 to, for example, the CH-53E.
No intermediate step at a Huey. Oddly enough, they seem to figure it out.
The monkey skill adjustment for me was the AFCS and the weight, and the significantly worse visibility from Huey to SH-2F.
I later went to the SH-60B, and cannot say I liked to fly that as much as the SH-2F, and that is due to the trim response on the Seahawk being less agile than on the SH-2F ... just as the Force Trim system in the Huey was more agile than the AFCS on the SH-2F. You do adapt to any new aircraft, of course.
T-6 as a primary trainer (when I was working JPATS issues) moved quite a few instrument flights into simulators, with good results.
Any new Army or Navy follow on to the 206 based trainer would be well advised to invest money in robust sims to move some of the instrument training into the the sim and out of the aircraft. Back in the day, helicopter sims were Crap. They have improved in the last generation or so.