Apart from Manchester City, other major teams have performed really badly in the last Premier League season. In the next season, those teams will want to build themselves up so that they can correct their mistakes and perform as well as Manchester City.
I don't agree with your assumptions, I think Arsenal and Manchester United had good performances last season, but they can't compete with teams who have a high level of consistency like Manchester City. Arsenal failed to maintain consistency due to the pressure exerted by Manchester City, but that's only normal because Manchester City is the better team.
Next season will be different mainly because these teams have built more quality from squad depth, but I think Manchester City are big favorites to secure the title. Arsenal, Manchester United, Liverpool, Chelsea and Newcastle have all the chances to end Manchester City's dominance, but the chances won't be any bigger than what Manchester City have so far.
Newcastle also appeared surprising this season because they have finished in 4th position to displace several other big teams such as Liverpool and Tottenham.
Arsenal did fail to maintain its first position but surprisingly also able to compete with Manchester City before, even in the first half Arsenal dominated the standings until almost the second half.
It will be more interesting to see some of the other Premier League teams have built their current squads to again thwart Manchester City back to the championship, but I'm not underestimating it anyway Manchester City will be a lot of favourites but who knows the season now there will be changes where other big teams will take over the trophy, I think it is still very possible.