The Premier League has very tight competition from other teams, therefore teams are required to continue to develop much better.
currently the most competitive league is the Premier League even though man CIty has dominated in the last few seasons but that is inseparable from the strength and consistency of this team which is very good.
Next season, Manchester City will get more difficulty to protect their crown in Premier League because logically Arsenal would become stronger, same for Newcastle United. Manchester United, Chelsea can get improvement in the summer too.
Of course there is no guarantee that Manchester City will be able to maintain what they have achieved this season, because other teams will surely improve themselves even better to navigate the new season to come. On the other hand, even though Manchester City is in very prime condition this season, it is not certain that they will be able to maintain it, because the decline in the team's performance will be unpredictable, we can see from what Liverpool experienced.