"Something changed in 2009-10, the question of what precisely deserves a separate investigation, when the number of goals scored in the top flight jumped from 2.48 to 2.77 goals per game. This increase has held steady bar a brief dip to 2.57 goals per game in 2014-15. The three highest-scoring seasons since the Premier League became a 20-team league have come in the last seven years."
- this would suggest that if the latter trio you mentioned have got worse overall, it's disproportionately more in defence.
I'd agree with that. Those 3 have become disproportionately worse in defence. At least that's my perception.
And I would say that though they have become weaker, they are not necessarily worse than the teams they have replaced in those 4th to 6th spots.
The teams we're talking about City, Liverpool, Spurs were always attack oriented. And whilst their attacks have improved, their defence has not become any worse than it already was. These 3 are scoring more goals against the rest of the league than they used to.
Additionally, the PL has become a top 6 vs everyone else. So when 'everyone' else plays each other, that's when they get their opportunity to put points on the board, and I think we're seeing a far more offensive minded game in (e.g.) Southampton vs Crystal Palace now than we would have done years past.
Not sure the defences are worse (apart from a decline at Utd, Chelsea, Arsenal) but that the top teams' attacks are better, and there's more focus on attacking play in general throughout the rest of the league because of the top 6 dynamic.
We already knew all this though. 1-0 in Serie A is 2-1 in the PL, to put things plainly.
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dude has no clue about football 
