To sum it up, I accidentally bricked an RT-N12+ B1 router by uploading a sysupgrade.bin through U-boot TFTP. I did not realize immediately that there was no factory.bin image in the first place on the Techdata page of this router which led me to this situation
The router can still go to the usual asus recovery mode by holding the wps/reset button and plugging the power source until the power LED starts blinking. Unfortunately, after many attempts at recovery through TFTP and uploading stock firmware there was no luck and router is still stuck on a state where only the power LED is on, the other 3 LEDs are off, no DHCP, even with static ip I cannot ping the device and LED indicator for Ethernet is off though it goes on whenever I make the router go recovery mode.
I've already tried recovering through the use of tftp2.exe, built-in tftp of Windows, and asus router recovery/rescue tool but yeah... no luck OTL I badly need help