I think it would be ok to turn off externals for df events, i only use them really for taking off and landing and sometimes identifying enemy ground targets, although not on SSS since the briefing was so clear
and for looking at my pretty plane.
only thing that might disadvantage some players is their lack of familiarity with internal only
to be honest, i think track IR users have a definate advantage in closed cockpit, and its maybe not fair to penalise people using externals to give the same level of awareness.
as much as an advantage as f6ing is, it still doesnt compensate for decent gunnery and flying....
my two cents