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Chasing Manchester United premier league win will be very difficult or impossible to achieve, atleast in this our time. 6 English Premier League trophies means 6 seasons and looking at it, the highest Manchester City can go before being dethroned as the indisputable champions of England is 1 or 2 seasons. If you look very well, Newcastle is just building and Manchester United is gradually coming back to form and Liverpool is there to always contest. There will be a time the reign of Manchester City will also come to an end.
I wouldn't say it would be difficult if Manchester City were still managed by Pep Guardiola in the next 10 seasons. Of course Manchester City won't be able to win the Premier League title in 6 consecutive seasons from now on, but I can imagine this team can do it in the next 10 seasons.
I see you said Liverpool and Newcastle are competitors, of course it is true and I will also add some other teams like Arsenal, Manchester United, Chelsea and Tottenham as competitors too. But Liverpool have not won more than one title since 1992, but Liverpool have managed to be a few runners up in different seasons. Chelsea, Arsenal and Manchester United have been far more successful since 1992 than Liverpool, and in the last 10 seasons Manchester City have secured more title than any other competitor.