So, I'm no expert and obviousy there are multiple volatility factors this election that makes it unpredictable, but that said...
I'd be a bit surprised if the Tories don't win.
1. Yes, Brexit isn't the only thing but it does seem to be a huge dominant issue. And while the Leave vote seems ready to coalesce around Johnson the Remain vote will be split between different parties to a much higher degree.
2. One reason for this is that Corbyn is so extremely toxic. Even though the alternative is Boris f**ing Johnson he's waaaay behind in popularity. And fundamentally those reasons are legitimate. I mean, when Al decides to leave the Labour Party that says something about the poor state they're in.
3. I imagine that for less political swingy voters who are a bit tuned out the promise to resolve Brexit with what can be sold as "not that dangerous" I'd imagine to be fairly powerful. My impression from many of my own British friends is that getting it settled and done as an issue in a way that doesn't feel scary is a fairly common sentiment at this stage.
There is obviously a lot more going on but I imagine those things will ultimately be enough to deliver a Tory majority.
