The Oerlikon 20mm/70 was a straight blow-back, there is no delay....
The Oerlikon and the MK-108 were straight blow-back designs. There is no delay between firing and the movement of the breech face. They did use rebated rims so the bolt could follow the base of the round inside the chamber and used a very long headspace to support the case longer, but that is not a delayed blow-back
A delayed blow-back design delays the motion of the breech face by mechanical disadvantage, as shown:
It is a matter of classification, but I thought the advanced primer ignition actions were classified as delayed blowbacks.
Toggles can be extremely stable, go over top dead center with a buttress on the links to prevent over-rotation, they aren't unlocking, no matter the load. If you look at any toggle lock design the toggle rotates to just over dead center and then stops, careful examination will reveal that they are actually .5 to 1 degree over center. The toggle will not break until the joint is rotated a degree or two.
Can you provide a link so I can have an idea of what you meant by buttress on the links?. I googled that and got flying buttresses.
I don't know if a degree or two is a tight tolerance or not for a fire arms mechanism. Intuitively it seems tight. You are right they have been used in a number of semi automatic and automatic mechanisms, and I assumed it was because it was easy to knock them out of alignment and get the toggle to break.