Dry hot climate better suited to asthmatics?

Actually no . Studies have shown that the dryness in the air actually intensifies asthma exacerbations and asthmatics do better with a higher relative humidity and moisture in the air. Of course there are different exacerbators for each individual with asthma.
Not necessarily. Long periods of hot dry weather lead to high ambient ozone levels. Ozone is a respiratory irritant and can precipitate asthma symptoms in susceptible individuals. Urban areas with hot dry weather also have higher levels of respiratory irritants like sulfur dioxide and diesel exhaust particles.