setup help design (Nighthawk(R) X4S R7800 or RBK53S-100NAS)

Hi all.  need some help

I currently have a FVS318Gv2 doing my dhcp and routing.  off this firewall / router i have a 24 port switch.

In the invironment i have a Nighthawk(R) X4S R7800 in ap mode.

The house is large and im not getting great coverage.  im looking at the  RBK53S-100NAS mesh system. (or any other recomendations)

My question is below.

The FVS318Gv2 is older and i belive it is limiting my download speed.  Im thinking of placing the R7800 in the basement off the cable modem for routing and basement wifi, and then putting the mesh devices in ap mode to cover the rest of the house.  which is a better router R7800 or the orbi mesh router?  Tnoughts? other ideas? concerns?

Thanks in advance!