I can not speak for every fiber provider or implementation, but I had Comcast Cable for a number of years, paying a premium for (at that time) 300 Mbps down and 60 Mbps up.   The stability was fairly good, and I did not really see any degradation during "heavy use" times of the day.   Then again, at that time my real-time use of the Internet was not extensive.  I usually did email and upload/download of modestly large files (few greater than 4 Gbytes).

At the same time a friend had fiber in Nashua, NH (about seven miles away) and was getting 1 Gbit sync up/down.  I was jealous, but it was not on the horizon with Comcast.

Then about five or so years ago Fidium came to down and offered fiber at 1 Gbit sync.  I ordered that and when they were installing it in our community I talked with the installer and he told me that it would be capable of 10Gbit sync in the future.

The 1 Gbit offer seemed to be "fast enough" and it was great.

Later I found out they were offering 2 Gbit/sec to new customers at the same price I was paying.   I called up and mentioned this.

"Oh, you are right"...then TWEAK TWEAK and magically I had 2 Gbit/second sync.

About that time my husband moved in and.   He started working from home and I found that he was using ONE TERABYTE of data every month.   Curious as to what was going on, I found that he was bit-blitting his workstation screen from Boston up to his monitor in our office (long, detailed technical story about why he felt this was necessary).  I had not even noticed this load on the fiber or on the routing system in my house (long, detailed technical explanation why I put installed this in the first place).

In the three years that he has been using "bit-blit" he is almost constantly in video contact with his co-workers (simultaneously with bit-blit) and I have other video meetings, watch YouTube videos, etc and no QoS issues.

There was once where we have lost service for an hour, but we received messages through cellular telling us about it and then it was fixed.   Other than that it has been rock solid (at least at the times we would notice it

There are things I might change (and maybe I can now, I just have not asked lately).

o Better use of IPv6.   I can use it, but they will not commit to whether I have full control over the low order 64 bits or just the low order 48 bits.

o Better use of my own Routers - they have WiFi routers that use load balancing in the WiFi for better QoS.   Of course I can put my own routers off theirs, but I currently have no use case where I strongly need that.   This may change soon.

o No static IP (at least not at my price point).  Of course there are ways around this.

All in all, Fiber is one of the best things that ever happened to me....it is very close to being the #2 "best thing", but that slot is currently held by Hugo, my husband.   #1 is being born.

md