You need more than just me to answer this but from an objective and factual viewpoint, there is more content and stuff to find and complete in Warmind.
The level and Power grind is more akin to what we'd expect and Mars is possibly the best planet to explore stuff on.
For me, its not huge changes (that's September) but 4 weeks in, I have plenty to do, 2 other characters to work on, raids and activities to learn and complete, guns to find, masterwork and challenges to complete. There's also July 17 free update drop to look forward to.
I have plenty of fun stuff to play in Destiny til September. That's the key though - its fun again.