Absolutely disagree about altitude as does biology. Oxygen saturation is real and does impact real time play on the field regardless of what's on the sideline.
It's actually a somewhat similar advantage as the temperature is in Miami for northern teams. On top of being unprepared for dehydration occuring as quickly northern teams have a difficulty with lower oxygen saturation that occurs at higher temps.
So with all that said, yes altitude is a competitive advantage but less for hot climate teams.