Whether or not you find it a grind is ultimately about your perspective and mindset. If you're just looking for pure monster fighting gameplay with multiple ways to approach it and challenge yourself, you won't find much better. If you're looking for a nuanced experience with multiple different ways to entertain yourself, you're not going to find it here, as it ultaimtely is just one striaghtforward gameplay loop.
I'd also be hesitant to really consider these games RPGs, as there's very few elements in the game related to the genre outside of weapon roles and equipment progression.
Think about the game like Dark Souls; cut out the character stats and leveling; and instead of a giant, open-ended, multi-sectioned, medieval-horror themed map, you instead access a bunch of separate hunting areas each large enough to have their own little sub-areas.
Gameplay mechanics are very similar, especially if you're familiar with the soul level one challenge for Dark Souls which is basically Monster Hunter. Both focus directly on gameplay challenge and a freedom for letting the player choose their approach to that. Both also focus very little on any overall story narrative, though at least with Dark Souls, you can find some if you're willing to look hard enough.
It's the type of game where you really have to motivate yourself to enjoy it, rather than relying on it dangling a bunch of interesting features, side-events or a compelling story to pull you forward. But once you get past that initial couple dozen hours; once you begin mapping out the type of role you want to play, the different weapons you want to try and find different ways to challenge yourself more and more, that's when it becomes addictive.
None of that even goes into the co-op.
