http://www.vg247.com/2014/07/28/destiny-beta-how-many-missions-strikes-datamined/
I'd say GW2 has around the same amount of missions for 80 levels. Destiny seems to be using a similar model where once you complete a mission, the next appears, but it's a few levels higher than what you're at so you have to go do other activities to rank up.
I like that there are that many strike missions. That's my favorite part of the beta, and it's good to see there will be more than one per planet.