When i was TTing back in the 80's i dont remember chain drop being a thing at all. Certainly not with a 5-6 speed corn cob anyway. As cassettes have got wider and chain ALOT more flexible it is definitely a problem even on smooth-ish roads.
I experimented with a non clutch Sram Force rear mech, on my 1x , and it was ok apart from changing gear onto the smallest cog. I watched it closely and the chain would get a whip on , in the horizontal plane , that would send the chain off the chainring. Otherwise it was ok even at an extreme angle , when in the lowest gear.
I ditched that mech and went back to the clutched mechs and no problemos. No narrow wide chainring required. To be super sure of not dropping i also fitted a wee ZTTO chain guide, but i have run without it and didn't get any drops. It mounts on a braze on mech mount, or an adapter.
Another thing in my favour is i use an 11 speed cassette , but i ditched the 11t. 50/13 is enough for 30mph at a sensible cadence and allows for some tweaking of the cassette position, for chainlines, if you make it narrower.
I suspect that alot of the problems, with drops, are actually down to the 10/11/12/13 speed chains being so flexible side to side as much as traditional chain slap being the reason.
I would put money on it that an old school chunky chain on a 6-8 cassette might be problem free off road as long as the rear mech has very good tension. No chain guide , no clutch and no NW chainring required.
Eta: on the subject of clutched mechs; in my experience, with Sram anyway, is there is an increase in resistance to pedalling. It isn't noticeable with your legs, but on a stand when using hands to turn the cranks there is a difference between clutch and no clutch. It is quite noticeable by hand though the marketing says not. Maybe this is why, even with drops being a problem, the road mechs used by pros are clutchless. Apart from Lidl Trek who were very successful in the classics with there road-mtb mullet setup.