Kalashnikov did an interview on the ak. During the process told the reporter that the 5.45 was a mistake. The Russians had to keep up with the Americans. Showed the 5.45 in ballistic gelatin compared to 5.56 and 7.62x39, not that impressive.
He told them the 5.56 is a good round and made for the AR platform. The 5.45 is ineffective in the ak platform. A small round must have good accuracy for combat. The AK was not designed for that. I don't know but will take the designers word for it.
I have several of the ebr. My first choice is always an ak in 7.62x39, then a galil or hk93 in the 5.56. .308 I like the hk91. I do have a few ARs just have a huge aftermarket support base so it's hard to stay away from them. My favorite AR is actually a 6.8 in a m-4 platform.