Both of which are seen quite a lot in AvA, scenarios, snapshots, and FSOs, not to mention EW and MW arenas.
As AckAck said, the MA is not everything that's out there.
- oldman (some may say it isn't even close to the best thing out there)
FSO/SE/AvA are obvious exceptions to the use of the He-111. I'm talking MA action only, sure the He-111 is a huge factor in the SE/FSO and sometimes the AvA spectrum, but what it boils down to is how much use it gets in the MA.
(I imply MA as the EWA, MWA, LWA.)
The IJN demanded insane range for a twin engined bomber. Mitsubishi wanted to go to four engines so they could provide armor and self sealing tanks, but the IJN wouldn't hear of it. In order to get the demanded range they had to actually do a wet wing for the G4M, where the skin of the wing is also the fuel tank, and of course they couldn't do self sealing tanks.
The problem I see in the He111 is that its tail, the easiest and most popular attack point for fighters against bombers, is completely undefended.
Glass nose + poor defense = bad day if cannons or even .50 cals are used. Frontal attacks will be just as fatal as rear-end attacks. If I were in the He-111 and I were taking damage from the rear, i'd try to turn myself so I can get my belly guns exposed. Rear end attacks are more dangerous if you can get the belly guns up to the attacker, but its unlikely for it to happen.