EA8300 poor download speed (upload is normal)

OTOH I don't think the EA8300 can get up past 350-400Mbps in typical usage (per 5Ghz radio).

The galaxy note 9 is 4x4 MU-MIMO and the EA8300 is 2x2x2 = you are only getting half the throughput the note 9 is capable of.

The TP-Link TX3000e is 802.11ax the EA8300 isn't.

I know the EA8450 is 802.11ax compatible. I don't know if it is a good match for you.

If you have a C7 it can do around 500Mbps according to the above link. It's 3x3 MU-MIMO so that makes sense. (ie. around 175 Mbps per radio). But it's not 802.11ax (WiFi 6).

The EA8450 is listed in the TOH as snapshot, (no stable release), so it is WIP.