The truth is that ALL 20mm cannons are packing too much of a punch.
If 6g of TNT equivalent is all you need to unmake a plane then why even bother with extra filler?
Why try 30mm cannons?
20mil is a middle ground
go below it and you recieve perks like more ammo or better ballistics but lose structural damage and requires more precise module hits
go above it and you recieve less ammo, less firerate and sometimes ballistics, in turn, you recieve the ability to slice planes with +20g or even 50g of TNT equivalent.
20mil just outclasses everything, almost structural damage of a 30mil with more ammo, firerate and sometimes better ballistics or quantity.
And I will say it again, every 20mil is different, 20mils are in their current state because people didn’t bother to look at explosive filler or even try to consider taking a different belt and then went:
“ThAT waS a 6 20MiL rounds!” Expecting a hispano to deal the same damage to a round with over 2x the filler because they just looked at the caliber.
As a result all 20mil damage was merged into one. And the one that suffered the most was mg151/20, not only because it was stuck with damage formulas for while, but because the upside it had of above average damage was given to everyone else.
ShVAK was helped the most because people now had essentially the old Mine shell with better ballistics and a full tracer belt of it too.
That explains the 2 mayor groups of people in this thread.
Then you have +30mil cannons, which the upside they had was that it was easier to miss due to reduced firerate or ballistics and more punishing to do so with a smaller ammo pool, They completely lost their place because
“Why bother?”
Aircraft with more than 2 20mils also lost their place because, “1 20mil does the job just fine!”
It was only later down aircraft history that the 1 20mil loadout was seen as effective because
1- Cannons are emergency tools now
2- The firerate ensures than at least a pair of rounds land somewhere vital.
If something similar to cannons happened to tanks it would be giving every cannon of the same caliber equal penetration, only difference would be shell selection and ballistics.
People didn’t accept than different rounds of completely different nations and gun lineages would be worse or better than other cannons.