I agree re: Arsenal, they have quite a thin squad, as do the teams they have competed with for fourth over the last few years. The top level teams though I feel are roughly on a par with us.
I think our definition of "squad" is probably slightly different. Mine is the best 14-15 player's outside of your "first XI" that are available at the start of the season. When we are talking about investment discounting player's like Marin, Lukaku etc seems disingenuous.
City: Dzeko, Garcia, Navas, Jovetic, Clichy, Dimichelis, Rodwell, Richards, Guidetti, Pantilimon, Milner, Lescott, Barry, Sinclair
Chelsea: Ba, Willian, Essien, Cahill, Lampard, Torres, Azpilicueta, Bertrand, Schurrle, De Bruyne, Romeu, Lukaku, Moses, Marin, Courtois
United: Welbeck, Hernandez, Jones, Smalling, Fabio, Young, Januzaj, Giggs, Zaha, Buttner, Fellaini, Lindegaard, Ferdinand, Kagawa, Anderson
I would say squad strength Chelsea are slightly ahead of United who are ahead of Man City by a bigger margin who are much stronger than Arsenal. I think because City and Chelsea have a much more consistent first XI, whereas United change much more often it gives a slightly skewed view; basically "Young plays 30 times a season vs Marin/Barry who've been shipped off on loan, the former must be better". Obviously if you discount loanee's then it isn't really a fair comparison in my opinion. Chelsea/City choose to rotate their team less and therefore choose to let quality player's go out on loan and if Fabio/Young/Zaha/Welbeck were on their roster they'd be out on loan.
I guess it's a relatively pointless difference of opinion though.