@ChrisD. You can't say "Stop blindly spending money on items which may not cure your issue." then come up with some more stuff like "OP will follow their own narrative and ignore all useful advice anyway." without even giving me a chance to respond to what Armageus said.
Whoever said the ping spikes were over wi-fi? It was ethernet. Pretty sure I mentioned that earlier but if not I hope that helps explain and I apologise for not being clearer.
My thought process being: Well the only stuff that has changed recently is more devices being added and since the spikes only happen when other devices are active even all idle on the network, it seems like a good idea to blame something that can't process data fast enough, the cpu. If it's 1am and others devices are completely off then no ping spikes. I was thinking like a quad core or whatever would more be able to handle those clients attached more evenly across the cores leading to less problems. Obviously thinking about it now it does sound stupid that the cpu on a router would help this but I just try to think of every possibility I can.
@Armageus I'll try to respond to your points if that's ok.
"A new router will not solve any range issues - all access points/wifi routers have to obey transmit power limits - there aren't more powerful units. Correct placement and quantity of access points is all you need to control."
I do understand this but again my thought process: The Smart Hub is ~2011 tech that tops out at 802.11ac (If I'm wrong on this my apologies). Now the mesh systems I looked at have 802.11ax as the wireless backhaul (tri band) which I believe has better range than the BT Smart Hub can ever have (between nodes anyway) because of this. I just place the 802.11ax nodes a couple feet infront before the wireless range issues are happening and since better range, it should then make those wireless deadspots not wireless deadspots anymore.
"Just No"
Not to be rude but can you elaborate on this? Why is the system bad for what I require? I did some reading on them and apparently you can ethernet backhaul BETWEEN nodes and not have to go through the router at all which then means cabling can be done much easier then.
"If you separate out your Modem/Router/Wifi, then you can upgrade each part independently as required."
Ordered the HG612 as you suggested/advised. Will be a good modular addition to the network.
Finally, Chris I'm not against taking advice. It's just if I see advice I want it to be backed up and explained thoroughly to see if it jives. To me "Just No" doesn't really help. It's like in the RAM section here and someone asks if 16GB of 2800C30 for £200 is good value for a 5950x CPU and I type "Just no" to the person then nothing happens. That person gets 0 value and nobody else that happens to read that also wanting to learn about RAM doesn't either. However, if I explain stuff like cas latency and how AMD performs best with 3200/3600 RAM and show reputable sources with benchmarks to corroborate the claims then everybody wins. That guy ended up learning and feeling well informed about his purchase and anyone else getting introduced to RAM aswell.
Like the "just get access points" stuff above. Well could you maybe recommend some models when you say access points are the way to go? Why this model? Good personal experience with them? Just little stuff like that you know.
Edit: So still no responses.