The whole idea about "how to fight a southpaw"- that being your left foot outside his right foot, throw the hook and straight right has been invented by people that don't and have never fought. When you are boxing, the idea is to get the inside punching position. By doing the above you surrender it. You put your lead hand- about 80% of your offense- outside his shoulder, where it can't land. You beat a southpaw by going to his left hand, making him throw it, then countering with left hooks or right uppercuts.
With Ortiz, you want him to establish that position- his right foot outside your left foot- because his left hand is weak, and because, and Berto hit him with this, once you go to his left he will flat turn around and follow you. He walks into the right hand. He got nailed doing this and went down, in the 6th, and Berto narrowly missed the same punch at least three more times. He was that close to winning.
They should have been telling Berto to slide right (not bail out like he often did) and hook of Ortiz's left, or make him turn and fire his right. Ortiz fought hard and clearly won, but he was never more than a punch away from it going the other way.

I didn't say you couldn't fight from there, I said the corner had no answers for the classic southpaw style. If you saw the fight you can't deny that was Ortiz's game plan and it worked. I agree there are counters to this strategy and the two mentioned can work but if you don't work on moving and pivoting right or you like to lead with your jab, problems arise. I see these issues every day as I work with a southpaw and he faces orthodox fighters that use this strategy in reverse. It can be frustrating to face as sometimes it limits your output.