Can't comment on the DOCSIS, I don't know enough about it to not be making stuff up.

Regarding WiFi though... The simple answer is if you're not having trouble accessing the WiFi in the places you use the WiFi and you're getting the full speed that you're paying for, there's not a ton of a reason to upgrade the router.

The exception to this is that most routers only get a few years of security updates like most phones... That can potentially leave your network more vulnerable as the router might not properly block unsolicited traffic from making it to your devices. There's a solid argument that you should just have your devices secured via their own firewalls though.

The Google routers are nice for the average Joe because they just kind of work and keep themselves updated (and Google tends to keep the hardware they sell under the Nest name receiving security updates a VERY long time compared to the competition). Netgear has been my go to for years but their update mechanism is ... fairly manual in my experience.

I've since moved to having a pfSense box for the firewall and routing side of things and using my old negate router in access point mode (I'm much less concerned about this setup).

I'll add that I don't recommend WiFi for gaming... And that most people have more download speed than they really "need." Files really haven't gone up in size much (sure games have) but evening else... meh (?). Video streaming is more popular but unless you've got a lot of people in your home or you stream at 4k, it's really not going to be that noticable between 30Mbps and 1Gbps. So like, by all means if you don't want to spend money, don't... you're probably fine.