As you see many Rayburn owners turn them off in the summer and make do
with an ordinary cooker instead. They only need to take a small logical
step to understand that this makes the Rayburn redundant as a cooker.
Not to mention that most Aga owners also have a collection of toasters,
electric kettles, microwaves, baby belling hot plates etc etc to make
up for the deficiencies of the Agas.
Rayburns were an improvement on the open fired range which in turn was
better than a fire in the middle of the living room floor, but things
have really moved on over the last 80 years or so. So it takes half an
hour or so to get up to heat - lighting and cooking on open fires can
be faster than that!
Latest models have added gas burners and electric ovens etc. They are
evolving slowly and will eventually perform just as well as proper
modern conventional cookers - which is what they will be!

cheers

Jacob