This should be an easy match for Chelsea, so I don't think a win will be a benchmark that Chelsea is ready to be in the top 4 this season. If Chelsea are able to beat Liverpool, Arsenal, Tottenham, Manchester United, Manchester City and Newcastle, then Pochettino can be said to be ready to bring Chelsea to the championship path.
Chelsea certainly can't drop 3 points against Luton and because of that they need to do well. Luton is not a very strong team so I don't think Chelsea has too much trouble winning the match. After all, Luton's confidence is not good after losing to Brighton 4-1 in their first match in the Premier League. If in the end Chelsea failed to get 3 points in this match, then it seems true that Pochettino isn't really ready to bring many improve to Chelsea this season.
It is not necessary to judge the weakness of Luton only by one defeat from Brighton. Brighton is a very strong team and I think many teams will be beaten on their field. Even though the bookmakers are giving Chelsea a very high chance of winning I wouldn't rush it, although I also expect Chelsea to win but don't forget that Poccettino is forming a new team we don't know anything yet about what capable of Chelsea.