If we're perfectly honest - No.
Reddit has over 53 some odd million users. Million with an M. Lemmy has gained, at most, upwards of just thousands. To call it a 'mass exodus' is really overselling it.
It's going to take a fairly long time, for Lemmy to even scratch 100k even. I'm on both Reddit and Lemmy. Lemmy, for a more positive experience. Reddit, because the numbers are just there.
The landscape was different. Digg was in 2004. Reddit in 2005. They both came in a time where social media was at it's infancy and it was anyone's game to make it big. Whereas today, there are already established social media sites and the best any alternative social media outlet can do anymore, is absorb some numbers and try to prove to be the better alternative. It's a lot about thinking outside the box and figuring what a platform can do that the other can't.