I'm on the end of the spectrum not bothered about weight (flat commute), I would rather have what I need for repairs etc...
My commute bike is 50 to 65 lbs loaded, depending on whether I carry my laptop, and how much food I bring for lunch that day.
I use panniers, not a backpack, it's easier for me.
I did a 500 mile bike camping trip once at 90 lbs total (not including my body weight), yes it's slower, but really, so what?
On my commute, I'm looking to do more work, not less, so it's a good trade off for me.
For weekend fun, I also have a 22 lb road bike. Fun yes, but it's easier to break something or flat, so I've never used it for commuting.
To each their own...