It seems to me sincerity is not the right word. Reading what your told to read and speaking off the cuff while expressing your opinion can both be sincere and present themselves differently.
It’s very likely that I’m personalizing this
I presented something this week where I didn’t have time to completely get my talk track down. It was an hour long presentation, some of which I read off a second screen above my camera
While watching her, she seemed much realer when not reading
I’m thinking the same was true of my presentation.
I’m hoping mine was nowhere near as noticable