I have Spectrum internet - fiber is not here in Dayton,OH yet.
Before I upgraded to their 100MB service ($70/mo), I had 15MB ($50/mo) and used ROKU (Premier+ model which is now discontinued) without much buffering.
Even with my 15MB service, I did discover modem and router can make a difference in performance.
Our little ISP just did an update and blew up a bunch of people’s dsl modems/routers and replaced them with big fancy things with three antennas. The little black box versions did better. I need to see if I can swap this one out for the old version. We could got to the 15mb plan for about $70 but we’re on a low budget right now.