It's sad that your stock firmware downgrade ended in a soft brick. Based on the AX3000T forum, I don't remember any cases where the downgrade of stock firmware was unsuccessful.
The good thing is that the AX3000T is a very durable device, and it's really hard to fully break it. There are many ways to restore the stock partitions.
So, be patient, connect via UART, post the terminal output here, and continue up to step 7. Before moving on, we'll need to detect your hardware (previously, all RD23 came with ESMT/Winbond NAND and the MT7531AE SoC, which is a reliable and supported by OpenWrt without any "but" like RD03 with Foresee NAND).
So, consider this a great opportunity to improve your skills. 