The difference between City and Inter Milan is so much, but the thing is that CL final's are always tough/tight, there is usually this nervousness and thought from the players about avoiding a mistake, so when you play by trying to be too careful, you'll struggle to perform at your utmost best, and that's what happened to City yesterday.
This should be exactly what was transpiring in their minds when they were playing the match. I expected Manchester City to be at their utmost best during that match but they were playing on an average level and that gave their opponent the privilege to understand the game more and make it more difficult for them to win easily.
Having said that, What Pep and his team have achieved this season is unbelievable, they have finally won the CL and they did it by winning the treble, i have said it before that City just needs to get one CL and many more would come, this is prolly the start of City's dominance in the CL.
Let’s watch out and see if that will be replicated since they’ve won their first UCL now. Pep Guardiola is still in the club so I won’t doubt their possibilities too much. But one thing is sure that champions league is hard to win than the domestic league, they need to be at their best always.