Good dual band antennas

I'm currently trying to debug an issue with a TL-WDR4300 and I'm wondering if anyone knows where I can buy decent dual band RP-SMA antennas.

These looks like the stock TP-Link ones, and I have to wonder if they are listed at 6dbi if the 5ghz gain is lower.
https://www.aliexpress.com/item/TP-Link-6-dbi-wireless-network-card-router-gain-antenna-free-shipping/1955149974.html

On the other hand I've seen these listed as 8dbi on 5ghz and lower on 2.4.
https://www.aliexpress.com/item/2-4G-5-8G-5G-8dBi-AP-Wireless-Network-Wifi-Antenna-1pcs/32673949482.html

The thing I'm trying to figure out is why my Netgear WNDR3700 can BLANKET the house at 19txpwr, but my TP-LINK TL-WDR4300 has garbage range at 21txpwr. Barely covers half my house. So my first idea is maybe crap gain on 5ghz with the stock antenna.