I mean, I don't consider giants to be all that crazy to begin with. It's well within the bounds of generic fantasy. Same with giant, hostile animals, people throwing fireballs and magic healing potions.
The guy gluing bodyparts onto himself for no discernable benefit needs an explanation. Like, something something acquire the powers of dragons... but he obviously didn't, and most of those body parts are from other people the same size as him or even smaller. It's not even at the level of 'I stuck my brain on the side of a giant' logic. It's just straight up 'lol, this is gross and this guy must be crazy!'
The turtle thing is far worse. He's the only one in the whole fucking game, so it's not like there's a race of sentient turtles and he happens to be one of them. And the fact that he talks isn't the only weird thing, they had to tack on that he's also the head of a fucking church, wears a fancy hat somehow AND he's an amazing spellcaster? Fuck it, why not make him a master swordsman and pilot of the world's only airship while you're at it? Give him a gun too, that'll make him memorable!
Lets not pretend this shit is at the same level in DS1. Probably the weirdest shit there is the covenants, like the talking cat and the wormheads and Frampt/Kaathe (at least those two are established as some kind of weird ancient race). Sif fights you with a sword, okay, weird. But she's also grounded in something familiar: A dog waiting at it's owner's grave, being territorial over it.
The design of ER was very clearly just coming up with random shit and shoving it wherever they felt things were a little empty. In DS1 you have various random monsters with the vague explanation of 'demons.' Flimsy, but whatever, demons are inherently a chaotic and random sort of creature, and they have a place they came from and are related to the flame of chaos. In ER you have shit that kinda fits, like the puppets made by mages and the bugs made from the rot, and you've got shit that doesn't belong, like the giant hands, a turtle pope, T-Rex dogs, worm faces, and so on. It's the mark of a team that didn't want to throw away any ideas or content they had, regardless of whether or not it fit with what they had. And even that could be excused to a point with excuses like them being illusions (painted world is a good example) but they just... didn't bother with so much of it. Like, there is no way in fucking hell the guy who designed that cool sword mage of rune fragments did it with the intention to have it left in a random cave with zero context. It was clearly supposed to be attached to some sort of boss or questline that was never finished. ER is like this woven rug that looks amazing in the middle and gets frayed and crappy once you reach the edges.