Nevermind.
After serching all posible solutions at night i figured out, that there is a version of this router mentioned as R4AC v2, so i just install firmware from one of my native language forums and it worked perfectly for me!
I think same version of router mentioned at this thread Xiaomi 4a R4ACV2 new version / bricked - #16 by Azello
So i think diffirence in this versions is mtd layout(as i mentioned - same as yours), and diffirent 5ghz chipset MT7613BE(i suppose it was actually a reason why 5GHz not worked for me initially)
Anyway, thanks for your help, your replys was my initial reason to not give up in my journey, and it actually ended well for me.