I agree with most of this, and I think this reality has sunk in for most people at this point. I think Clinton will have a slight lead again next week, and I'd still favor her to win based on how I think Trump will perform in the debates and the ground game in the fall. But he's got a real chance to win, and that should scare everyone.
Only thing I disagree with is the Sanders comparison. Sanders is the only serious presidential candidate I can remember that was never truly subjected to negative campaigning, because Clinton initially didn't consider him a threat and then later had to worry about courting him and his supporters.
I'm sure the polls would show Sanders up a bunch on Trump right now, but I'm also sure they'd paint a much different picture if he and the RNC had spent the last few months dragging him through the mud on his socialism and the VA scandal and whatever other lies and half-truths they could peddle. Not to mention all the moderate left-leaning female voters who were bitter about Obama in 2008 who would be apoplectic if Sanders had gotten the nomination in 2016. I think he'd still be outperforming Clinton, but I'm not convinced it would be by a huge margin.