Current router config:

ISP router 

Routed LAN to WAN into TL MR 100 for cellular backup 

MR100 configured in wireless router mode 

MR 100 LAN to WAN into Archer C6 - configured in access point mode 

Finally 

RE 200 as a range extender 

All wired and wireless connectivity coming off the C6 

All working wonderfully (and didn't set up with the intention of mesh networking) but RE 200 mentions in but provides error that base router doesn't support it. 

Presuming the base router being referenced is the base of the TP Link stack (TL MR 100)... would the only way to enable mesh to be to get a new router at that level 

The C6 also supports it