I'm just of the opinion his reputation outweighs his ability. Happy to be proved wrong, but I base a lot upon gut feel (probably stupidly) and his time over here never warmed me to his skills....
Thing is with the likes of Mancini/Ranieri/Di Matteo (and to some extent Koeman I guess), people judge them on having done okay at huge clubs. I just don't actually see evidence of any of them being especially good managers though. I think Poch, had he been in charge of a Chelsea or a City, would have won the league fairly easily because I think he is a talented manager. Those three are sought after to a greater or lesser extent because they've worked at big clubs, rather than showing great ability (in my opinion anyhow).
(Slightly different with Koeman as he's actually had greater success growing smaller clubs, which is why I'm happy should he be appointed here).
Di Matteo aside, these managers would have got opportunities because they performed well as a coach/manager at clubs at Southamptons level or lower. The game is opinions but I think we seem to be shopping in the right market. All the managers linked have good pedigree across Europe. I'm pleased we're not going for an up and comer from the lower leagues
People trying to find an unexpected 'winner' and the bookies cutting the odds to draw money away from Koeman. Money is being absolutely lumped on Koeman and at current he's the only one with concrete backing to it, and would appear to be leading the chase. By bringing odds in of others, with punters placing the odd bet to trigger it, with Gross, Magath, Ranieri, Sherwood, they draw money away.
I think Ranieri has done very well and he tries to develop or add value to youth. Look at the young players he brought in to Chelsea when he was there, even if all of them did not make it in that side. So I think he is a far stronger candidate than someone like Di Matteo.