Your set up, withthe hall having thethermostat and its radiator having no trv, is correct.
Turn the hall radiator manual valve right down. Then the rooms will get up to heat and their trv's will control them, and the hall will come up a bit after. With the boiler being on to keep the hall up to temp, it will be on enough to keep your other rooms warm. Once the hall stat is happy the boiler will go off, and then you're right, the hall has to cool down to bring the boiler on again.
It isn't a perfect control system but unless you have thermostats in every room, its about as good as you'll get. Th eopening of the hall rad valve is obviously a question of balance.
The only improvement I know of is to put a trv on the hall rad as well, but it must be set just over the temp set on the hall stat. Then the hall can warm up as fast as the rest. When the house is up to temp, all the trv's will be part closed, including the hall one, because the rads stay hot after the stat turns the boiler off and there's a temperature overshoot. The overshoot in the hall turns the boiler off, but when the hall temp drops a little and the boiler comes on again, all the rads including the hall's are part closed so the boiler stays on a bit longer (than it would have if the hall rad had been a manual one) so the rooms stay up to temp better.
That (somewhere in there) is the theory. Whether it can be made to work I haven't got the foggiest - I've never tried it. And what shoots all the theories to hell is that everyone and his dog (and cat) leaves the doors open all over the house.
