As someone who flys a lot of WWII and has done a fair bit of game engine development, if all that is designed in, it just isn't working at all in practice.
HE/Frag
Flak should be a shrapnel effect but it seems to be treated as a HE blast, anything in the radius gets damaged, if it's close enough you take damage to every surface and every part of the engine at once, yet weirdly the pilot is almost always totally fine (see below). It's all or nothing from a frag blast, when it should be like a shower of light frag, ironically the most danger is to the pilot.
With everything using the shilka algorithm they also all get modern radar gunnery, even through cloud without any kind of radar director, that can make it crazy effective as direct AAA too. Real flak direction was horribly ineffective needing thousands of rounds and area saturation per kill. (although late war allies did get radar flak, usually on warships 5" secondary batteries)
Penetration
The AP 20mm just don't penetrate, if you hit the tail it shows damage to the tail, hit the wing, regardless of angle, hole in the wing (doesn't do much). If you fire up into the engine or kick the rudder to shoot in from the side it will fairly easily knock out the engine but it I've not seen it penetrate through the aircraft to the engine as a 20mm AP easily can.
The seat armour in the german fighters can just stop 0.50cal, a 20mm can penetrate and turn a chunk of that armour into shrapnel. The pilot wouldn't survive. An unspotted bounce was just as deadly from a SpitfireIX as from a 109k4. But you need to hit from specific angles to make it do anything in DCS.
We rarely see those rear/underseat tanks get punctured or ignite when hammering the rear of aircraft that have them. Self sealing tanks only do so much, with allied incendiary rounds in tests detonating those around 30% of the time (some cool guncam footage out there). It'd self seal vs machine gun calibre ball, AP or frag, but only up to a certain size, it shouldn't self seal a 20mm hole.
Rear Damage Cheese
Top axis players in pairs have a strategy of just ignoring fire from the rear to drag even for very close in aircraft if they have friends nearby because of this, one 30mm will end the allied aircraft before the 20mm can destroy him (if at all). Often they don't even need to go home or fall behind after this.
I've been able to ignore hundreds of hits from the rear in 109's as I run. If they're out of 20mm there's no danger at all. That close 6 position is an almost guaranteed kill in reverse. It's clearly not correct.
HE is much more powerful as it effectively ignores armour. Wherever it hits anything in the radius gets damaged. Negating armour. The opposite of how it should work, armour is strong vs non-AP damage. The german HE/frag was strongest against wooden soviet aircraft. The 30mm admittedly is big enough that tails coming off isn't unreasonable.
Spar Damage
But 20mm hispano to the wing root should equally weaken the wing spars enough that the wing would be off under most flying conditions.
In thousands of hours I've only seen wings come off the Spitfire. And I think that's usually just an effect of it being very sensitive to pulling more than 5g at >400mph rather than damage.
I'm also not totally convinced the german MG's aren't being treated as HE rather than the micro frag damage the really do.
Skin damage creates some instability but doesn't noticably affect speed. The drag penalty from all the holes we see in a fuselage should be very signifcant. Small aerodynaic differences make large max speed differences, so a big holes or even lots of little ones should be bad.
Pilots
Pilots kills are extremely rare even with masses of clear hits down into cockpits from or through the sides have no effect at all most of the time. Even 303's have no trouble penetrating glass and thin side walls or pilots, but in the game we joke they're just BB's for tickling. The only ones I commonly see are on the Anton. Other aircraft pilot kills are basically never happening. So the pilot hit box is tiny, isn't working most of the time or the glass/side skin is stopping them for some reason.
Ground units
Ironically the same guns are very effective at longer ranges vs much more heavily armoured ground units than they are vs fighter aircraft.
I don't think it's so much that the 20mm hispano needs a buff, I think penetration isn't being modelled and things that are actually frag are being handled as HE pressure radiuses because the shell is called HE.
The damage model you describe just isn't working.
Are we pretending this doesn't go through a light fighter?
