Signal ingress due to outdated neighborhood phone props

Internet plan: "Download as fast as 600 Mbps" - $152/month

Location: San Francisco, CA 94127

Modem:
Voice and Data Modem
ARRIS GROUP, INC. TG3482G
Serial #: 14C03E97E191

Context: I am living with 2 other people; they use WiFi and I use direct Ethernet connct.
The setup is 1 Ethernet connection to Google WiFi points & 1 Ethernet connection directly to my laptop. For purposes of this discussion, I'm excluding performance of my roommates. I am only discussing problems I'm seeing.

Connection: Ethernet (CAT5E) with Belkin USB-C (supports 10/100/1000BASE-T)

Representative sample: September 29, 2020 at 11AM - 12:36. Average of 100Mbps (Ethernet), 29Mbps (WiFi). Paying for 600 Mbps

I've been experiencing poor internet consistently for the past few months. To define poor: I'm paying $152/month for "download as fast as 600 Mbps". Since I'm connected to Ethernet, I define poor as anything less than 200 Mbps performed on https://speedtest.xfinity.com/ at any given time.

I think I've eliminated a few options:
* WiFi is NOT the problem: I've been Ethernet connected on CAT5E cable with an adapter that supports 10/100/1000BASE-T. My MacBook Pro is 2019.
* Data caps are NOT the problem: We have 1229GB data cap but have spent at most 749GB in any given month.
* Running on or off VPN does not matter: I've tried both PIA VPN and without a VPN
* DNS choice does not matter: I've tried both 1.1.1.1 and ISP-provided
* Device is NOT the problem: I've tested the Ethernet connection on another laptop. I've also tested WiFi speed on my phone & laptop & they're both performing
poorly (in WiFi case, poor can be defined as < 50 Mbps performed on https://speedtest.xfinity.com/)

I read a few posts on the forums (e.g. https://forums.xfinity.com/t5/Your-Home-Network/Internet-slows-to-0-5Mbps-randomly-and-frequently-throughout/td-p/3323876). At this point,
I believe the problem has to do with rented modem hardware or street cable (correct me if wrong):

* Modem is outdated or incorrect - PingPlotter is reporting some packet loss. I'm familiar with the software so not sure what to read - https://imgur.com/a/uprdVXz

* Connecting between modem & outside is faulty - http://10.0.0.1/network_setup.php gives me some output but I'm not a network engineer so not sure what to look for -  https://imgur.com/a/hjzEWFK

At this point, I believe I have to contact Comcast Support to send a technician to fix hardware issues. Does the forum have any idea on what might be causing this internet and if contacting the technician is the right next step? Cheers!