It would be daft to knock Savelio simply because he is both dynamic and still has the potential to develop further. But I suspect TS was faced with a dilemma; give him a 3yr contract at a decent salary (£45k ?) on the assumption he will indeed realise that potential. Or to stick with Currie / Hughes / Julien as the prime choice BR with perhaps Livett and Wilde if injuries threaten the first choice. TS could probably offer Julien a rather modest package ( ? 2 yrs £30k) simply because this is his first full year in the BR. And while Savelio / his mum / his manager seem very demanding (based on the Saints background), Julien by contrast appears far more willing to earn his place at the top (taking a share in student flat at Padgate for his first year).
As fans, we tend to just look at the ability of a player, but if we were managing we would also have to balance the salary cap between the squad and would also be much more aware of those players that are 'high maintenance' (e.g. Sandow).