Plenum rated Ethernet unless that duct is really an electrical conduit and not and airflow duct.

QOS policy being run on Arris G34 router ? Or bad firewall config?

Get a proper router that you configure and then throw the G34 into bridge mode

https://arris.my.salesforce-sites.com/consumers/articles/General_FAQs/G34-G36-Bridge-Mode-Setup/?l=en_US&fs=RelatedArticle

I suspect the problem is that when you put your switch in , it’s going to be faster because of a misconfiguration when you try to use the G34 as a switch

You can configure a router to prioritize small packets (gaming) even if you’re in a high upload or download scenario. I have 120/10 and my son has single digits pings in Fortnite even if I’m doing a video call and screen sharing and my other kid is watching YouTube . This is one way to QoS.