Latias is a critical member of stall and defensive teams. Latias acts as a great mixed pivot thanks to its resistance to grass, water, electric, and fighting. Latios lacks the bulk to do the same thing. Calm mind isn't for outright sweeping, latias isn't suppose to, calm mind is used to sponge special hits better and beat out some special attackers, and at the same time if you keep your Latias around, you can very easy pull a late game calm mind sweep due to its speed and ability to boost and not be easy be taken out by anything. Latias well be getting more use anyway now because of it's ability to combat Keldeo and Thundurus, another example of it's utility.