Sorry for the late reply, I was waiting for stuff to arrive.
I've managed to get a solderless serial connection working using @jeff's and @mk24's tips!
As I suspected I was falling the product id verification test:
original_product_id = 743d2275
original_product_ver = 74662d38
recovery_product_id = c7000002
recovery_product_ver = 01
auto update firmware: product id verify fail!
While I was waiting for the image with the proper header values to compile, I decided to try @newbee's method and to my disbelief it worked! I was expecting issued with TFTP as before but it all went fine.
After flashing DD-WRT, I just simply rebooted the router into TFTP and flashed the "factory.bin" from here: [GCC 7.2 BUILD] Optimized TP-Link Archer C7 V2 AC1750 LEDE Firmware and my router is now back from the dead!
I wish I could mark all your answers as solution as they all played a crucial part in this adventure!
Thanks for all the help! 