It's really not a big deal in terms of time if you just go in and pick them once (ditto for ADRs).
When you start trying to optimize everything, that's when the planning gets time-consuming.
I think that first-time visitors are probably benefitting from FP+. It's encouraging them to do that bit of pre-planning that we all know can help make a trip better. It's a bit better than walking in and pulling out a park map.
I also think that people who go frequently don't mind as much. If you know you will be back this year (or ten times this year), it's not a big deal and you might appreciate the prescheduled FPs.
It's the people in the middle....who don't go frequently (1x a year or less) and
who knew how to ride a lot of rides and enjoy a lot of rides in a day....those are the people who don't like FP+ from what I read here anyway.
Just my theory anyway. Planning is the eye of the beholder
The key now is to be willing to pre-plan as much as possible AND be flexible when things don't work out as you planned when you are actually there. This is really asking a lot of people!