Personally, I don't think the card should be buffed by giving Momentum. All the dragons are meant to be vanilla creatures (as in creatures without abilities), and it should follow that rule.
But its attack power cannot be buffed satisfactorily either because of Stone Dragon.
Colossal Dragon - 10
, 7|15
Stone Dragon - 10
, 8|10
Massive Dragon - 11
, 8|30
Basalt Dragon - 12
, 10|12
If Colossal Dragon's attack becomes 8, it will be the same as stone dragon except that Colossal has more HP, therefore a lot of people are gonna shout imbalance.
Similarly, if Massive Dragon's attack power becomes 10 or more, it will have 18 more HP than Basalt Dragon.
But then again, if you compare creatures of certain elements, you can see imbalances where the creatures have the same cost/HP but different attacks, etc.
Blue Crawler - 3
, 3|3
Horned Frog - 2
, 3|3
Theoretically I can argue that Earth has an easier time accumulating lots of quanta since its cards are cheaper than Gravity's. However, I'm not sure if that reasoning's actually gonna work out.