Yes, if Osvaldo and Ramirez had settled better we'd be a better team and yes, if Yoshida was a better player our squad would have more depth. But they didn't and he isn't. I don't think that's just down to luck either, the club made judgements on all those players and luck doesn't really come into it (maybe it does a little in the case of Ramirez and his injuries).
so, it does or it doesn't? 
There is an awful lot of luck involved. There is also an awful lot of careful consideration and scouting, but do not think for one minute there is a single guarantee in signing a player.
FYI, I am not one of the ones who think we'll break into the top 4 in a year or 2. I predicted 8-12th this year and we will do that; I hope for an improvement again next year, but that will be very tough indeed.