I've had a Note 8 for a couple of months and experienced no lag, and honestly couldn't tell you what is different in Facebook between iOS and Android. That is coming from years on iPhones and last two years on a 6s+.
There is nothing wrong with the default Samsung messaging app. There are other choices of you don't like it. I like most of Samsung's software. The issue with messaging is that iMessage is proprietary and does back to MMS for non Apple devices and MMS sticks. This is the biggest annoyance with Android, if you message with a lot of iOS users. My whole family has iPhones but e have worked it out.
Zero of the things on your extensive list have been a problem for me on the Note 8.
To the OP, I have throughly enjoyed the Note 8 and Gear S3 so far. It's the most fun I've had and most excited I've been with a smartphone in years.
Apple will need to really do something significantly better than the X to have me moving back to an iPhone.
Probably the only sane and sensible reply in the thread lol.