I looked into it and it looks as though safeloader converts a stock image to a sysupgrade compatible file, so its easier to move to stock from openwrt. There is a website which converts the images: https://argsnd.github.io/tp-link-stock-firmware-converter/index.html
I'm not 100% sure the safeloader will help.
Can you try the tftpboot again but try
tftp ${loadaddr}