I really don't see why you'd want to change from Sony to Nikon as from a quality of the kit standpoint it would seem to be a backward step. Maybe even only a slightly backward step but maybe at best not improving on what you have. I can really only understand switching to Nikon if you're a very hard core Nikon fan and simply must have one or if there's some handling or menu foible that's driving this... or maybe just GAS, pure and simple?
One thing I sometimes do when I think I'm limited by kit in some way is look at what other people are doing with the same kit and I usually change my mind and decide the problem and limitation isn't the kit, it's me
Just on this forum looking at the Nikon and Sony threads I think the best pictures by far are in this thread. I suppose that doesn't tell you too much about the kit, all it really tells you is that some people who are good at all this use Sony kit
but at least it shows you what's possible with the Sony kit.
To be honest I'm struggling to see any compelling reason for anyone to switch from Sony to Nikon or Canon mirrorless at the moment. It's up to you, but I do hope you give this careful thought before going through the whole process of switching gear again as you might find yourself wondering why you bothered.
Just my 2p Andrew
I hope you give it careful thought.