I'm in complete agreement with the grass/electric pivot that is needed to make a successful CAP able to tackle rain and sandstorm, making holes for that under used grass type to exploit.
Momentum is a critical issue in weather and the ability to turn that momentum around by defending and threatening common water types and ground types will make for a reliable 'check'/pivot. It is not weak to earthquake either, but neutral, being a grass type. Useful when in a team that has a lot of ground weaknesses.
Dragon/Grass is still extremely susceptible to ice, no matter how you spin it. It is not just a momoswine with ice shard we need to worry about but with rain having the ability to hold defensive cores it can reliable harbour and use choice scarfers with ice beams/etc that waters do enjoy for coverage. It will simply increase the importance of ice coverage in rain teams.