I love both, the Souls series and DD, I'd be playing DD online if I could. I played DD vanilla, and Dark Arisen... got all the achievements. I've played that game three times one after another and when the PC version came out I bought it too and play it sometimes, although I prefer playing on console.
I agree that the monsters look kind of mundane, but that's also the intention of the devs, it's mentioned in the artbook: they looked into historical records of how some monsters were supposed to look, if you pay attention, harpies in this game look like the pictures you find in history books, while harpies in Dark Souls are pretty weird and freakie. Gransys itself look like a place you could find in our real world, the only fantasy-like setting that tried to remind you that it was a fantasy game were the weird springs with magical water, the rest of the world looked so plain and mundane it could very well be our own world, and it worked for me, I fell in love with Gransys and wouldn't change a thing about it.
The combat in DD is more flashy and less realistic than Dark Souls', but I prefer it much more since you feel like you're fighting a 'real' creature, rather than hitting the nails of a dragon until it dies. The pawn system was also pretty unique and fun, having a pawn with you is the equivalent to have a Black Iron Tarkus or a Jester Thomas with you all the time, since they are very useful, especially when you find though groups of enemies.
Dragon's Dogma is flawed, a lot actually, but it's so much fun I don't really care about its flaws.
Now, about Dark Souls III... haven't played yet the DLC since I want to finish Persona 5 first but I think I have played enough of vanilla DSIII to give an informed opinion: The game is great, the combat is as fair as ever, the magic system still needs more work this time than in previous entries, but I love it; the main problem the game has is that it's my 5th Souls game... I know where an ambush is waiting for me, where there's a hidden trap, I can predict as well what I have to do to find shortcuts and hidden paths and secrets the very first time I visited an area because I played the other 4 games a lot, I already know what to await from the 5th game. I'm not tired of those games, it's just I have a lot of experience with the previous ones than wathever they throw at you, you already experienced it. It's better to let the series rest for a while and they know it very well. When a dev knows there's no reason to keep a series going for so long, you have to respect their decision to take a break, and so right now we need more Dragon's Dogma and less Dark Souls.