The comparison is valid, but not from the perspective you are seeing it from. From my perspective, I *do* spend many, many hours grinding in dark souls. I really, really like the game and enjoy taking it very slowly. I think my only full completion took about 26 hours, and many weeks' worth of playtime. Totally worth it. Rogue Legacy falls into the same category as I don't mind the grind at all. I'm not really playing it to beat it, but rather for the entertainment.
I grind a ton in Dark Souls too. Here's the difference for me though:
Dark Souls gives me reasons that make the grinding worth it. The drops, the monsters, the bosses, the secrets, the treasures, the progression, the environment....all those keep me grinding when far saner individuals have just said no.
Rogue Legacy, on the other hand, is different. It has all those elements too....but I just don't find them super compelling, because I don't think they're designed very deeply. The drops, at least at the start, aren't interesting. The monsters are one note. The secrets are few and far between, I feel like. I found an invisible wall my very first game, didn't see another one in 50 lives even trying to find them. The treasures....take a while before you're like "oooohhh" "aaaahhhhh". The progression, while being simple, is also very grindy and it doesn't have a lot of trickle down effects that make you think hard about what to get or what it does for you. You spend the majority of your time thinking about how much stuff costs and if you really need it, than mechanically what's going on.The environment is decent, but there's not a ton going on aesthetically that I find interesting and in a 2d side scroller I find boring backgrounds pretty unforgivable. I was like "Aw yeah, 2d sidescroller with kickass backgrounds like Symphony of the Night!" The reality is pretty uninspired. And the whole character art style, from the beginning, wasn't something I was a fan of.
I CAN see the appeal in the difficulty of the platforming and how that dovetails the grinding in an enjoyable way. Just not for me. The action doesn't really thrill me so the difficulty doesn't appeal to my sense of challenge. I'm not saying it isn't appealing or doesn't appeal to some people's sense of challenge...it just doesn't to mine. I sort of need the game's supporting features to make me interested in the main action, and I feel like most of the supporting features are adequate at best, minimal at worst. RL feels a lot like an arcade game to me, which is why I have a hard time getting invested in what it asks me to do.