Yes when you are using motorised TRV heads there is no real need for motorised valves so wiring them both to one wall thermostat/hub would seem a good idea, however Hive does have a problem I am lead to believe, it will not accept a demand for heat if the wall thermostat is over 22ºC so one does have to select an area which will not get two hot.
Although in theroy when using motorised TRV heads you don't need motorised valves to split the heating into major and sub zones, I note the Drayton wiser does just that.
why there is a three channel version I don't know, also the boiler can be independently controlled from the motorised valves when using OpenTherm
so how it is wired can vary, with most thermostats it seems to be either motorised valves or TRV's the EPH has thermostats that can be set master and slave so again independent wiring to motorised valve and boiler when using OpenTherm.
However the budget Hive does not have an OpenTherm option, and some boilers like Bosch are not OpenTherm enabled, and even if they are I am not convinced it is required. For that matter not even sure a wall thermostat is required.
Unless living in an open plan home or using hot air central heating we are unlikely to be able to control the whole home with wall thermostat/s. Mine has 9 electronic TRV heads which control the temperatures of the rooms independently from each other, however there is a small problem, if we get a warm day, the boiler will cycle on/off all the time until I turn it off manually if I did not have a wall thermostat.
So we fit wall thermostats to stop boilers cycling, that is all they are normally for.
There are exceptions to every rule, I have one area of my home, I will call it the flat with 4 rooms only used in summer and when we have visitors, so having a motorised valve to turn off all 4 rooms makes sense. But at the moment sitting in my bedroom, so bedroom TRV set to 20ºC and wife in living room also set at 20ºC but kitchen set at 18ºC and dining room set to 12ºC, craft room and office set at 14ºC wife's bedroom at 20ºC the hall has the master wall thermostat set at 18ºC and the hall TRV set to 17ºC so hall will not get too warm and cause the boiler to stop running.
I don't have opentherm as using an oil boiler which does not modulate, so for me likely Hive would be better than the Nest I am using as unlike Nest Hive does connect to the TRV heads, but before wiring in any thermostat you need to work out what you want it to do. This will change with different home layouts, different boilers, and different life styles, I am retired so want heating 24/7, but if I was working likely I would arrange heating to switch on in a sequential way, kitchen, dinning room, living room, then a lot latter bedroom. And maybe use geofencing, although my attempts at using geofencing have not worked very well.
So what are you aiming for?