I don't underestimate Chelsea but I think Chelsea need a few more seasons to become a solid team whoever the coach builds a solid team is not easy especially if they rely on young players, Manchester City is a clear example of how Pep Guardiola builds a team and now we can see the resul. Another reason Chelsea isn't the only team to transform there are other teams that do the same like Arsenal, Manchester United and Newcastle meaning that the team that has better progress will get the first place I mean these 4 teams have the same chance.
I agree with you. Chelsea needs time to return to their best form, it won't be very easy and suddenly perform with their best again. Although they can perform well in some pre season matches, they may get some difficulties when they play against strong teams in EPL matches. There are many young players in Chelsea squad now, they need an adaptation. Moreover, there are many new players in the current Chelsea squad, their performance can be not really consistent enough when the new season begins.
In this season Chelsea made many big changes, especially in this transfer window where Chelsea sold many players who performed poorly in the previous season and gave a lot of assumptions that Chelsea will start a new era with Pochettino next season.
Chelsea have sold unnecessary players and signed some players who can fit with Pochettino's tactic/strategy. Sure, it is a big change, Chelsea will begin the new season with many new players and a new coach. Let's hope that Pochettino can make Chelsea to perform consistently in the next season.