Quick background, I work for an industrial combustion system manufacturer and do gas system design for the ignition systems on our equipment. I wanted to knock my PB's plumber upside the head when he installed the gas line to the pool pad because he put a regulator on the heater and when I questioned it, he wouldn't listen to what I was asking. I was not being rude, or trying to imply I knew more than him, bc I don't do residential and there is plenty that I don't know. I just kept asking him what things were for and telling him I didn't understand because the manifold was only at 9" WC, not 2psi as he kept saying. Long story short, I had to tell the PB that the line wasn't going to work and they got him back out and he had to redo all of his work.
Most likely the gas company installed the reg at your meter. And I'll bet the plumber that installed the reg at the heater did the same thing that my plumber did, was note the MAOP of the meter, not what pressure was coming out of that regulator. I would get a plumber out and discuss with them and make sure you and they both understand if that reg is needed. My guess is that it is not. My pool heater will run with an inlet pressure of 4-14" WC, and I would guess that most heater manufacturers are set up like that. Because most residential installations are set up for 8-14" WC outlet at the meter.
Regarding the gas flow issue, my initial meter was only rated for 250,000BTU's, and I had a potential demand of 630,000BTU's before I had the pool heater installed. Potential demand after adding pool heater and fire pit went up to roughly 1.1million BTU's. I called and asked for more volume, they sent a service guy out, he tried to talk me into jumping up to a 2 psi system, but that would mean I would need to install a regulator at my gas manifold in my garage, or at every user, and I didn't want to do either. So he threw a larger meter on there.
Realistically, I will never get near that 1.1 million level, as there are several gas drops that I am not using, such as the dryer, indoor fireplace, garage connection. But the potential is there, so I wanted to make sure it could handle it. Pool heater seems to work a little bit more efficiently now, not a lot, but what I don't have is the outdoor fire pit flame sucking down when the pool heater kicks on. Because I have enough volume to handle them both at the same time.
As RPHpool suggested, give your utility provider a call. Mine was happy to throw a larger meter on there so that they could sell me more gas. Most are.
--Jeff