So many of these sorts of fighters in MMA these days, and its a really bad idea. A lot of guys look good on the bag in their unnatural stance; it can even help you in that your dominant side is closer to the target so you lead leg kick, jab/hook are improved. But whenever someone is a boxing gym actually tries it in sparring its terrible; you'll can't move as well, your balance is crap and worst of all your defensive reflexes pretty much shut down. Sanchez was being hit with punches he could see from a mile away. And being hit flush, in the middle of the face.
All your points are true, trying to strike, especially box from a converted southpaw stance make most MMA guys more stiff and awkward. I should say though that there are a decent amount of examples of it working. Most of the guys who make it work in MMA do it because they learned to stand strong foot forward in some sort of grappling. The guys who make it work in striking only sports tend to just give up their rear hand for either a great jab like Moorer or great hooks like Cotto and De La Hoya. LeBanner made a good career out of it, and Schilt is a switcher, but mostly southpaw for the sake of that nasty jab. Very few guys can make strike as converted southpaws in MMA, even some of the ones that do it fairly well still look akward. Anderson Silva and Lyoto Machida are two guys who strike very well from a southpaw stance, they switch a lot, but most of the time they are converted southpaws; the guys who can do it with some success but look awkward are Franklin, I think he's the best example of it, Diego, and now Mir, who still looks awkward despite two good results striking from southpaw. One guy who manages to strike very well but uses the stance because of his wrestling background is Kid Yamamoto; he looks pretty natural with a huge lead right hook that KO's people, but stands that way because he has been wrestling that way since he was born.
A couple of times when he got rocked, Sanchez instinctively switched to orthodox, then got hit more and had to consciously go back to southpaw. Its different with guys like Silva and Machida who are specialists and have the muscle memory of 20 yrs training; what I'm talking about is guys who probably learned how to fight southpaw in their 20's and look so unnatural doing it.
