Yes. I read over and over people trying to state/claim that FP+ has no real detrimental effect on standby, and say it's been proven based on a study that Touring plans did back in 2014 after FP+ was introduced showing little change in standby lines. But that study is flawed in that it compares the effects to standby between FP and FP+, not FP+ vs no FP at all.
We have some good data now though when you compare standy with FP+ (in 2019) vs now with no FP at all. And you also need to take into account that there is less to do overall in the parks right now (no parades, no character M&Gs, fewer shows etc.) so more people are queuing up for rides vs other activities too.
As an example, here is 7DMT wait times the 3rd Wed in July through Sunday for 2019 (with FP+ in full effect) vs. 2021 (no FP at all and less other activities available as well that even out the crowds better). 2019 was consistently higher for Standby than it is in 2021 with no FP. The same pattern shows for pretty much every headliner I check and compare.
View attachment 596201