I'm at ~30 hours or so at the moment, but i'd still say around 40% of games ends with a leaver after 7 minutes. I can definitely tell that players are getting better (people countering melee and properly denying souls, etc), but the leaver problem still remains.
I can also tell you that the post-game rewards from dota is on average worth less than €0.01, so that is absolutely not what keeps them there. The actual reason is that you leave 2 games in a row and you get low prio. If you've spent >1k hours ranking up, you're not just gonna make a new account when you get low priority, so the only people that do leave early are people that lose their internet connection or account buyers.
This game is so new that the most amount of hours anyone could have is 100-200 on the high end, so a lot of people who come to try it out don't really give a fuck about rank and will probably just permanently drop the game if they leave enough to get low prio.
With that said, it's definitely more fun than dota. Perhaps I'm just getting tired of the hyper-competitiveness of ASSFAGGOTS-games but I'm enjoying my general deadlock-experience more than dota for sure.