Well then, please define "tight".
Air between the notes adds punch!
A tight performance = a punchy mix
If the tracks you get to mix aren't as tight as you would like ,... you probably wont get as good a mix as if the tracks were recorded tight.
Every song is different and sometimes you just have to do the best you can with what you have to work with and hope the next tracks/songs are better,....
Not every song you get will sound the way that you would want it to sound...