I will answer this question based on Pokemon learning Draco Meteor in general.
Draco Meteor, in my opinion, kind of depends on the type of move you like. It depends on if your Pokemon is a special attacker or a physical attacker, as well. If your dragon has high special attack, then Draco Meteor can be deadly. Just keep in mind that it sharply lowers your special attack, so it won't do nearly as much as before if you use it a second time, which is why I personally prefer Dragon Pulse instead of Draco Meteor on a special attacker (it also has more PP). It also depends on what you want to use the Pokemon for or what the Pokemon should be used for. Like Redshift said, Latias is a bulky Pokemon, so you may not want to use him for attacks like Draco Meteor, whereas Latios is a good sweeper, so you would probably want to use Draco Meteor on him.