Yes Buffalo over performed last year so you can expect some regression to the mean.
The defence was very strong last year, and is bolstered by greater experience for guys like White/Hyde/Poyer, as well as bolstering the D with starters and depth players like Lotulelei, Edmunds, Murphy, Phillips and not really losing anyone. So theoretically could be a top 10 defence.
WR was our major weakness last year and has been bolstered somewhat with new additions and more experience for Zay Jones.
Offensive line will struggle with losing three starters, and will be our weakest area, and could hamper the overall performance of the O (and subsequently the D). But with some additions, or some over performance, they could be decent.
I can see the ups and downs roughly averaging out, and the regression to the mean pushing us back to 7 or 8 wins.
After the first three games, we aren't exactly playing superstar defences who will put massive pressure on the O line, other than the Jags. So if we grab a win in the first 3, I can see roughly .500 from there on, which would land around that 7-8 win mark.
Josh Allen was the 14th quarterback in the Super Bowl era to throw three touchdowns and run for two more in the same game and joins former Dolphins quarterback David Woodley as the only players to do it during their rookie season.
Bills have fired three minor coaches - ST, WR and OL, which were pretty much the team's three major weak spots this year. Not sure I'd blame the coaching but it's starting anew with players and coaching personnel in 2019.