Liverpool are expected to strengthen their squad next season. Next season, Liverpool, City and Arsenal will probably fight for the title again. However, if the performance of Chelsea and Manchester United improved, the Premier League would become more competitive. These two teams are far behind.
You have a point Manchester United and Chelsea are far behind compared to how they were few years back. Chelsea have shown some sign of improvement towards the end of the past season and if not because they Sacked Pochettino Chelsea should be able to challenge for the title as well because they have been gaining back confidence and their balance.
Next season the competition might not be as exciting because even if Arsenal still try to win the title we all know they won’t be able to win it unless Guardiola leaves Manchester City. Manchester City might see less competition because Kloop have left Liverpool and they’d probably lose more players and it might take time for the new coach to adapt to the league and the players.
We should not just conclude on next season and we don't need to use what happened in previous seasons to give final results of what will happen next season. Arsenal last season point gap from Manchester city as not as closed as this season. This shows a good improvement than previous season. So it is likely that next season, Arsenal might win the trophy if they remain consistent.
Chelsea should have not sacked Pocchetino and they should have given him another opportunity to see if he will revive the club because I saw some improvement on the team towards the end of the season. Chelsea was in a mess last season and two coaches managed Chelsea, so I don't think why they believe that Pocchetino will use one season to fix the club, when he is not a magician but a coach.