I'm trying to understand why using this wifi bridge arrangement gets me 300mbps on an internet speedtest but connecting to the same AP from a PC using an intel AX210 wifi card only gets to ~100mbps on speedtest (google).  

The network consists of a spectrum router (600mbps service) downstairs connecting to the EAP225 access point upstairs on Cat6 cable.  Then the PC and WA3001 (client mode) are about 25 feet away from the EAP225 and are physically about 6 inches apart so there's no difference in obstructions. Both see the access point as a strong signal. 

The PC will get ~100Mbps when connecting directly to the EAP225 but when going through the WA3001 it will get 300Mbps.  Are there some settings to make the direct wifi card connection better? I can see in the EAP225 management page that the link speed for the WA3001 client is much higher (650mb) than the PC wifi (175mb).  I see a google pixel also getting high link speeds so I assume it's something on the client side that is preventing it from performing as well. 

I'm using the wireless bridge to connect a local ethernet lan in the office with a few systems on it to the internet so they use the GB ethernet to communicate between them but also have them also visible to the wireless devices in the house. 

Current arrangement: 

[Spectrum router] --- [EAP225]   ))))))  [WA3001] -- [SWITCH] -- [NAS]

                                                      ))                                        |__[PC1] (300mbps to the internet)

                                                      )) [misc wireless]               |__[PC2]

                                                                                                |__[PC3]

Prior arrangement: 

[Spectrum router] --- [EAP225]   ))))))  NAS

                                                       ))) PC1 (100mbps to the internet)

                                                       ))) PC2

                                                       ))) PC3

                                                       ))) [Misc wireless]

In both arrangments there are a bunch of other miscellaneous devices like tablets, phones and smart home devices also connecting directly to the EAP which haven't changed.

There is no speed improvement in the old arrangement when all devices but the one PC doing the speed test are powered off so it's not related to the number of connections.