Losing to Manchester City is bad but not the end of season because the opponent is a strongest team in Premier League recent years. The point is they shown very poor performance in that match and there is very little signals that they will be able to play better in next matches. Their fans have negative reactions and feel disappointed because of this reason, not only a defeat by a strong opponent like Manchester City.
During the era of roman abrahimovic, Chelsea are mostly signing only proven players, not players that will come into the team and be experimenting to know if their level and quality is up to the standard of the club, as at then, anyone that is being signed into the club, they expect him to deliver immediately, because he is already a proven player, not this nonsense Todd boehly is doing with the club.
While in this Todd boehly era, Chelsea are just wasting their money signing unproven players, youngsters that they are not even sure that they have what it takes to play an succeed at the top level, and all this stupid decisions and signings from Todd boehly is what have kept Chelsea like this, because almost everyone in the team are average players, unlike the roman abrahimovic era when Chelsea only sign players that are ready to compete, not amateur players.