I lived there and I lived in many other cities like Paris, London, Munich, Krakow, Bangkok and Bali.
Venice is one of the most authentic cities of them all.
The language is alive and evolving.
It's a bit like the fight club, real locals recognize each others, while the tourists think it's just a Disneyland.
Quite fascinating!
Charming restaurants, quirky bookshops, etc., that's not "authentic life." That's frivolity. Sharing frivolities with the locals doesn't give you any insight into their "authentic life." Tourism is always Disneyland. It's always fake. It's just different versions of Disneyland for people of different temperaments.
(It's funny you mention Bangkok. I was born in Bangkok. What exactly is less "authentic" about it than Venice? How can a city even be less "authentic" than another city?)
But then I saw a couple traces of authentic life. We ran into a local walking her dog, and my friend (who speaks fluent Italian) chatted her up. On one of the smaller canals I saw a road sign -- not seemingly aimed at tourists or even gondoliers, but at ordinary Venetians trying to get around.
All of a sudden, the whole city felt amazing.