I think the biggest thing that will hurt Dauntless is, if you want to play a game to hunt down big monsters, you can either buy a full game from a well known successful franchise...
Or you can buy an unfinished game from an unknown developer.

So there is definitely a risk there for your average consumer.

The thing that OP mentions

one is a paid game and the other is a Free to Play title, so people who didn't have the money to play Overwatch got an alternative

Is not the case at the moment.
Dauntless is not free. Not now. Mark my words if it is not made free at least a couple of months before MH launches on PC, Dauntless will not survive, as much as I'd like it to.

Dauntless already missed out on having an open beta before MH launched on console. There's already 2 people I know that quit Dauntless to play MH on console.
That's 2 less players in a game that is already lacking in players.