Chelsea have not started the season well. They lost the first match against Liverpool. But I was quite satisfied with Chelsea's performance in the first match, even though they were beaten. Chelsea's performance was good. Their match strategy was also quite good. But their performance further deteriorated in the second match against West Ham. They conceded 3 goals and lost the match. And the main reason for Chelsea's poor performance is their poor defence. Had Chelsea's defense been stronger, their performance would have improved. I don't think Chelsea's match strategy is bad. And Pochettino should do his best to tighten up Chelsea's defence.
Chelsea's last game against Liverpool ended in a draw and like you said they performed very well. They also had other outstanding performances against Luton Town but they struggled to beat AFC Wimbledon and lost against Nottingham Forest. The defense is not solid because they keep conceding avoidable goals and some fans criticized Thiago Silva for his underperformance in the game against Forest. Another problem is that the attack is not also getting the needed goals. They create many chances but end up not scoring the needed goals.
It is still too early for Tottenham to really be stable even under the new management of Ange Postecoglou. Because Tottenham will go through a long Premier League process, the twists and turns of the challenge will not be as smooth as at the start of the season. And if you look at the big clubs Man City, Arsenal, and Liverpool, of course this needs to be reconsidered because Ange Postecoglou is still in the process of testing Tottenham and you could say he is conducting an experiment, so he is not yet completely stable.