I've had Sony Xperia phones in the past and to be fair, they were pretty good and reliable. It's just that their marketing and strategy in terms of phone releases left a lot to be desired. I can see a lot of LG fans transitioning to Sony. If they market this phone correctly which is a huge if, then I can see this phone being a hit. That being said, I might get it as my second phone.
That's been the basis of smartphone industry over the past decade. Companies are and should be trying to push the envelope constantly - you're right about the 4k screen resolution but with more 4k content available and 4k being more widely adopted than Quad HD, 4k screen resolution will be the standard in 5 years time.