There are two issues:
a) I'm still jetlagged and a bit distracted after vacation, which means I forgot something rather important
b) You've erased u-boot
GXL (S905X) and newer boxes look for a magic boot header in the 1st sector of emmc or 512th sector of emmc or SD or USB, but older GXBB boxes like WP2 only look for it in the 1st sector of emmc (or 512th sector of SD or USB). The problem is, the first sector is also where the MBR partitioning data lives, so you have the choice of partitions and no-boot, or boot and no-paritions. Amlogic "vendor" u-boot implements a custom offset-MBR partition scheme to workaround the design mistake (which is corrected from GXL onwards).
If you connect the UART cable (WeTek did ship them with the box) you'll see it endlessly looping with something like:
"GXBB:BL1:08dafd:0a8993;FEAT:EDFC318C;POC:3;RCY:0;EMMC:800;NAND:81;SD:0;READ:0;CHK:0;"
It's not bricked. It simply means it cannot find the magic boot header. The normal way out of this is to write the "wetek-play2" image to an SD card and leave it connected. It will then boot from SD and you can tweak things to store data on emmc if desired. In your case the SD slot will not permanently latch/retain the card, but you'll need to figure out a temporary way to hold/fix the card in for long enough to boot from SD and perform some remedial steps. I would start by zero'ing the emmc (the z option in emmctool) and then "dd" u-boot.bin.sd.bin-wetek-play2 directly to /dev/mmcblk1 (no offsets, seeks, etc.). This will put mainline u-boot and the magic boot header in the 1st sector, so the box will boot from emmc, and u-boot should find the "wetek-play2" image on a connected USB stick.
The alternative is putting the original vendor image back by writing Dropbox - backup-wp2.img.gz - Simplify your life directly to /dev/mmcblk1 and then rebooting. This is a raw backup of my box taken a couple of years ago .. but should work.
Apologies again .. I'd completely forgotten that GXBB has the extra hoop to jump through.