If Alonso had chosen RBR instead of Ferrari, is there any doubt they'd have signed him in an instant?
Or Button... or Hamilton... or Kimi... or even Schumacher?
Vettel might have the advantage of the best team, but calling that 'luck' would seem to be silly. The most 'luck' that Seb has had in his 4 championships came in the form of Vitaly Petrov putting on the drive of his life in 2010 and keeping Alonso from his third championship.
Alonso made the choice of not having the Adrian Newey car. If that's all it takes for Vettel to win, then Alonso chose to lose.
Otherwise, we have to acknowledge that the sport is one of the most complicated on Earth, and it's demeaning to F1 to dismiss a four time champion as 'lucky'.
The other greats ended their careers when they had nothing left to give (either in terms of skill, or desire). In the long run, it is this reservoir of skill and desire that determines who is 'great' and who is merely 'excellent'. Vettel's place in history is still being written