To my mind the job of the wall thermostat has changed, in my last house the boiler had no by-pass valve, and did not modulate, it was an open plan house and up-stairs would get warmer than down stairs, especially if you left open a door, as heat raises.
So one wall thermostat down stairs by the arch between both rooms, with no TRV's down stairs, however there was a Myson fan assisted radiator by the front door with thermostatically control fan, and upstairs we had TRV's to stop rooms over heating.
[it's not an exact science but varies from property to property]
This is very true, we are told the wall thermostat should go in a room normally kept cool, this means on a potentially warm day the boiler does not fire up, with no alternative heating, so kitchen is out, on a lower floor as heat raises, and with no external doors. I don't know your house, but not such room in mine, or any house I have lived in.
Ideally we could place the hub/thermostat where ever we wanted as the TRV's link to it and tell it when the boiler is required, but looking at the price of Honeywell EvoHome, Drayton Wiser, and others, most of us want some thing a little cheaper, no a lot cheaper.
So basic idea is the TRV controls room temperature, and if we want a sequence, we can get TRV heads like eQ-3 and Terrier i-30 which can be programmed, and I in 2019 paid £15 each for bluetooth eQ-3, only really NEED bluetooth if two radiators in the same room, but it does may setting them easier, although will only connect to one phone.
But the TRV unless linked which are expensive, can't tell the boiler to stop or start, so we need a wall thermostat, and careful setting the TRV and wall thermostat can work together, but without careful setting they can fight each other.
We really want a room or space which is heated 24/7 or at least heated the longest, in mothers house the hall was selected, the hall has a problem, when front door is opened it cools rapid, so needs a large radiator to recover, but unless we stop it, that will cause the thermostat to switch off prematurely getting the rest of the house cold.
The TRV was lower than the wall thermostat, and other side of best room door, closer to front door, so it was always cooler than the wall thermostat, but a standard TRV has around 2ºC between starting to close and shutting off completely, so if TRV set to start closing at 17ºC and wall thermostat set to 19ºC since it is higher, it will switch off once whole house is warm, but the hall can recover fast, but not trigger the wall thermostat too early.
I call it near enough engineering, with a modern modulating gas boiler with a by-pass valve this set up allows the boiler to gain the latent heat by turning down output so the radiators stay warm rather than alternate between hot and cold, and so reduce the hysteresis in each room, and since I have done it, I know it works.
However when I tried to repeat it in this house with an on/off oil boiler, it didn't work, in the main due to hall taking too long to cool, I can adjust how fast a room heats with the lock shield valve, but I can't control cooling time. Also leaving doors open or closed changes the characteristics of the room, and sun shine though windows can cause temperature to sore.
Two identical houses either side of street, are not really identical, as the sun will shine through different windows, so you need to consider your house, not simply say this is how it is done. And also of course consider your pocket.
The hardest thing I found was setting the lock shield valves, clearly throttle back too much and room does not get warm, but open too much and the radiator over shoots, the TRV is slow to act, 12 noon every Saturday my TRV heads exercise the valves, to stop them sticking, so open fully, close fully and return to setting, this takes around 3.5 minutes, so radiator needs to take at least ¼ hour to heat up, if not more, as otherwise the TRV can't close or open fast enough.
