I found my gas cylinder pressure also dropping quicker than I expected.
Either I didn't keep track of time properly, or something else is going on.
(No leaks, I checked the cylinder valve itself, the regulator, and finally the outlet hose.)
Also, I don't really remember, but I recall my gas cylinder had a higher pressure than 200 bar at the beginning, like somewhere near 245 bar.
At the beginning I made the foolish mistake of not tightening the regulator with a wrench (because I didn't have one), and thinking it would have been sealed properly.
So opening the valve, quite a lot of gas escaped at the beginning.
After that I tightened the regulator with some other tool that wasn't really suitable for it.
I only bought a wrench later.
(Anyway, don't make these stupid mistakes like I did. I just wasn't familiar with this kind of technical stuff at all.)
I think the real starting pressure must have been something near the 250-270 bar range.
It would be nice to get some more information about this from someone who understands this better.