Manchester City are no doubts still the defending champions for the premier league next season and can win it again. They were able to show last season that they can perform consistently all through the season. They won the league last season because they were clearly better than every other premier league team, not because there were no good teams in the league. Manchester City had no problem winning the premier league last season and will not also have a problem this season if they can play well, they dominate the league already. The league that will give them a problem, were they are not as sure as winning the premier league is the champions league. They may not be able to defend it.
I don't know how far your research has reached to give you the outcome of saying that Manchester City will still be the winner of the following season in the Premier League. What I want you to understand is that just because they won the league last season does not guarantee that they will still be the winners next season. However, I don't know if you forget that other clubs are also going to battle in the same competition in which you said Manchester City would be the winner. Arsenal, Chelsea, Manchester United, and Liverpool are also looking for these trophies, and they are almost 100% ready for the season to arrive. Don't be surprised if the club you underestimate is the winner or topping the sport when the season arrives.
And I believe the season has yet to begin for us to anticipate who will go and who will be left behind, so I believe we should wait and see. However, don't be surprised if Chelsea, which had a dismal season, comes out on top the next season; this is football, after all.