They are better than us and frankly at almost the half way stage they've almost already wrapped the league up, and will be deserving winners when they do eventually win it (barring a massive but unlikely collapse).
However people need to compare the differences in Squads that Mourinho and Pep inherited - Pep had players like Sterling, Aguero, Silva, De Bruyne at his disposal - that's a world class attack and that's what separates us from City. Pep's done well by shoring up the defence, but it's not the hardest thing to do since defenders are cheaper and you can get the best for £50m a pop. Mourinho on the other hand has had to fix a midfield that's been dying ever since our great 2008 team, and he's done well thus far with Pogba and Matic. Our attack is also severely lacking options - Lukaku is a good start but all our other options are either potential (Martial/Rashford) or average (Mikhi/Mata/Lingard). Keeping players like Welbeck, Nani etc around might have helped us by having some experience/other options around, but they were sold. The thing with Mourinho is that in every club he's been at he's been good at in the transfer market, I'm sure he knows we need options in the wide positions, so hopefully he addresses it in Jan/Summer.
Once we get those attacking options in we can go to toe to toe with City, but right now they've had a big head start with the attacking options they already had before Pep arrived. If we even had half of the 4 City players mentioned earlier we'd be nearer to being equal to them. Hopefully in 2018 we get 2 top wide players and a top midfielder and then we can really challenge and won't be hampened creatively when someone like Pogba or Matic are injured/banned. Mourinho obviously wanted Perisic so he's aware we need wide options, but hopefully the gulf in class between us and City sees him really making it a priority to get some top attacking options in. Price wise we might also see less competition, teams like City, PSG, Liverpool are all pretty stacked with attacking talent so we could get some good deals.