How does that prove the 'wrong' person won? If I remember that original job was only a years minimum contract. Hes also still working with Amstrad which says something.
As far as Simon winning, while I do think Kristina would have been better suited, Simon was also a decent choice. Simons big error in the shopping challenge with the trampoline wasnt something he would be doing in usual work anyway AND his choice of the wheelchairs was the choice which earned the majority (if not practically ALL) the cash on his team.
But both were completely viable choices, both actually did well in the task despite some egging on by Simon with promises, something that matters little in the long-run of things. Maybe the only thing that tipped it in Simons favor was the risk-taking which SAS seems to prefer more over more conventional styles of work.