I see another possibility. The gap under the F of WIFI is an inline component in an inner layer of the multilayer PCB. The boost in dB from the “screwdriver test” was antenna gain… but in what band? Could have been your local AM station. You can test your theory with a trimmed paperclip jumper with L ends. Lay some electrical tape on the PCB, then put the trimmed paperclip jumper in place. I predict no improvement in your wifi performance.
Touch a 20 cm straight wire to pin 2 of the Realtek chip and see what happens to your wifi bars. The core (assuming an antenna coax cable) of the RF antenna connection on the Realtek wifi/BT chip is pin 2. Coax braid to ground. (see page 11 of the spec sheet in your link).
I would solder a coax pigtail terminated in the usual wifi RF connector to the Realtek chip. You then connect a stock wifi antenna (USD 5 on eBay) for tablets to the connector. Page 10 of the spec sheet has a pix of the Realtek chip. That would be a great mod… that I’ve never seen done before.
.
