I use to have an upright Dutch bike with a derailleur as well as a nearly identical one with 5 speed Sturmy IGH. When we were riding with guests I'd ride the derailleur version, otherwise I'd always ride my IGH. I noticed no difference in the two. In an attempt to have a lot of upright IGH bikes for guests we've amassed a collection of about a dozen different IGH's and all work quite well.

There was a very slight noticeable difference with the early Nuvinci's but not nearly as much with the current ones. Even so I still really liked the variable gears and ride one of the new ones today.

Both Netherlands and Copenhagen went through brief periods of derailleur popularity. These didn't last long and people were back to IGH which overwhelmingly dominate. If they were a problem this wouldn't happen. Fixies have lasted longer and are still popular with a small portion of the population but probably make up way less than 1 in 1,000.