@TCDoe 

This is the guide you should use for building WDS with Archer C7 v2.

When building a WDS you should bare in mind that:

"In order to build a successful WDS connection between different devices, it requires that both devices use the same wireless MAC address format.For example,Site A uses 4-address MAC Address format in passive WDS bridge mode,Site B also uses 4-address MAC Address format in active WDS bridge mode.

WDS may be incompatible between different products (even occasionally from the same vendor) since the IEEE 802.11-1999 standard does not define how to construct any such implementations or how stations interact to arrange for exchanging frames of this format.-----From Wikipedia"

If you have configured the C7 according to this guide, C7 WDS status is "Run", but you still have no internet access when connected to C7, then probably the culprit is your main router.

You can check if that's the case if you try building a WDS with another main router (another TP-Link router, just not from AX series).

  @TCDoe 

I doubt that C7 is defective. I've seen problems building WDS with AX series routers as a main device.

That's why I recommended testing C7 with another router which is not from AX series.

As for the RE450 - it's not the same as using the C7's WDS feature, so with RE450 it should work out of the box.