I see your point that it's mostly the same group of players as last year but you know how much football can change in a short amount of time.
You've gone from not losing a single game to the the rest of the top 6 last season, to already having been thrashed twice and only winning 1 out of 5 so far.
Let's go down that particular rabbit hole:
Last season:
@ spurs 1-1
@ city 1-1
Home vs arsenal 3-1
Home vs United 0-0
Home vs Chelsea 1-1
This season:
@ spurs 1-4
@ city 0-5
Home vs arsenal 4-0
Home vs united 0-0
Home vs Chelsea 1-1
So, they were better against arsenal this year than last year, they were actually better against united this year than last year, Chelsea missed a penalty to win it late in the game last year but overall both games were pretty even(in fact liverpool probably looked better last year)
They lost badly to city after Mane was sent off -last year they were quite lucky to escape with a draw as well, and the game wasn't much different than what happened this year 11vs11
Spurs away is the only game where there was a big difference in their performance compared to last year, if we exclude what happened after Mane's red card(which effectively killed the game)
Their record from last season was mostly true to their performances, but also quite lucky. They consistently got the breaks in games were they were being outplayed(OT, Etihad) and never got suffered too much from the breaks that went against them in games were they deserved points(Chelsea penalty, Arsenal coming back from 1-4 and putting up real pressure late...)
So while they were the best team overall in matches against the top 6, they were quite lucky to go undefeated in those games
What happened so far this season is a regression to the mean -they no longer got the breaks in their favour
Where have you been the last 4 year when Madrid won 3 CL titles with a shaky defence? Madrid and Barca have dominated Europe with their attack.
Historically great attacks. Barcelona had 3 of the 4 best players in the world in 2015. Last season, we scored in every game we played. In 2014 we actually had great balance. Dortmund aside, no one else truly troubled our defence in the KO stages, and we played Bayern in the SF.
In 2016 we were just extremely lucky