Don't expect similar performance from Liverpool next season because they're not the only club in EPL. I don't think that any club can do what City did. Other clubs will also tighten and strengthen up their team by bringing in new players. I might be wrong but I don't see it coming. City is getting strong and Arsenal is also there to be in competition with Liverpool.
What you said certainly makes a little sense because in every season all teams that have money will continue to spend the best players to improve their team's strength so they can compete with all rivals in the Premier League. I also agree with what you said that teams like Manchester City and Arsenal will still be quite difficult opponents for all other teams next season, not to mention if there are surprises from teams other than them such as Newcastle and Nottingham Forest. So clearly there is no certainty that Liverpool will be much better than this season in the Premier League next season.