Hi, I dont know much about the signal levels, but i would say 100% get another router and put the superhub in modem mode! I did and its the best thing i ever did. I Started with an Asus router, and it solved all my wifi from dropping out, devices constantly losing WiFi and being booted, Baby cameras freezing all the time, It was the SH3 that was causing the issues. It just isn't a very good router when it comes to heavy usage.
The Asus had a lot more memory in it and a processor, and this fixed everything! Since then i have updated to a Mesh network which is made by Ubiquiti Unifi.
I now run the unifi security gateway router, and a 24 port Hp managed switch and a load of unifi access points around my house and in the garden. Best thing i ever did!
The Asus router also did increase the wifi coverage as well when i first did this, enough to make me realise how bad the SH3 is. I decided to go full out on the unifi kit because our house is basically made of lead and the WiFi sucked upstairs and outside no matter what i did. Now i have 5 Ap's and one of those is outside in the garden!
here is the router https://www.amazon.co.uk/UBIQUITI-Networks-Security-Gateway-Router/dp/B00LV8YZLK/ref=sr_1_5?adgrpid=...
here are the aps i have in the house
https://www.amazon.co.uk/Ubiquiti-Networks-UAP-AC-LR-802-11ac-Dual-Radio/dp/B016K5A06C/ref=sr_1_2?ad...
and i have some of these as well
https://www.amazon.co.uk/Ubiquiti-Networks-UAP-AC-LITE-Access-Point/dp/B016K4GQVG/ref=sr_1_1?adgrpid...
and this is the outdoor ap that gives me 300+ Mbps in our garden
https://www.amazon.co.uk/Ubiquiti-UniFi-AC-Outdoor-Mesh/dp/B01NAAWOGO/ref=sr_1_6?adgrpid=52905490773...
** ++ Superhub 3 (Modem Mode) - Vivid500 - Unifi USG - Unifi Access Points - HP Procurve 24 managed switch - Netgear GS108 Switches - FTP and Plex Servers - NAS Drives ++ **