In my opinion the move to mirrorless can result in less parts, less cost, possibly longer life span and a more direct path from image to sensor. It will upset the folk that insist on a view of the image TTL (through the lens) but as processing speeds went up over the years I think mirrorless models with a viewfinder are a really good idea.
I won't miss all the noises that occur when the mirror moves inside the camera. I'm sure you won't either.
Your slow to focus comment is mildly interesting. When we move up from point and shoot models we may want to manually focus. Low light focus speeds are always slower. Not much to discuss here.