No need for coaches at all for 1800 or 2000 otb.
There is a surplus of study material for any serious student.
Hanging around some stronger players can be very helpful. That's all we had anyway, for a couple decades starting in the early 70s. Some lucky few had a mentor, but that was still less than a coach.
I think anyone who is motivated can reach 1800 otb minus a coach, unless they're pretty old or just don't have the time.
in another word that is easy to get to 1800 here without coach but hard to get 1800 otb and is better to study/get coaching to get there.