Could be. my diaphragm is rubber with a metal disc in the center.
On the 109/balanced adjustable, there is a rubber (maybe some synthetic rubber) purge cover with a metal disc (it has the SP logo) but all the diaphragms are silicone. I've never seen a SP reg with a diaphragm that's not silicone. Not saying it doesn't exist, just never seen one.
Getting back to the OP, there are only two possibilities; the lever height is really low or the purge mechanism itself is not working correctly. If the lever height was really low, that would likely make inhalation effort really high. I guess it's possible if there was a wrong style lever in there, it could be too low for the purge but not so tight as to affect the breathing effort. That's probably a long shot.
Anyhow, it's easy to check. Adjust the orifice so that it just barely does not free flow without the diaphragm in place. There should be basically no play in the lever, maybe just a bit. Then put the diaphragm on and cover and see if it flows. If so, you have to tighten the orifice and drop the lever height. If you have to do that substantially, like maybe more than 1/4 turn, there's a lever/poppet incompatibility issue. But that's more common on a 109. Most of the G250s I've seen have a lever that works fine with the s wing poppet.
If when you put the diaphragm in place after adjusting the orifice, there is a lot of play between the diaphragm and the lever, that probably means you need a new lever.
This is assuming the feet are catching correctly with the tabs in the poppet. I've never seen one breathe even close to normal without them being lined up right, so I would be skeptical that this is his problem. But you never know.
