Yes, the allowed RPM are too low. It is also too sensitive to temperature - you should be able to take off with closed radiators and I certainly cannot do this.
However, I can still reliably take off and have a blast (literally!) without worrying overmuch about the temperatures or RPM. See below my takeoff procedure (note that there are annotations which don't seem to work on mobile viewers).
The only time this has failed in the last 20 takeoffs was when I forgot to open the radiators.
I'll link to my level bombing guide tomorrow. Still uploading...