It is dreadful. Especially galling on PC where we are supposed to have a choice. As for DS, lol, playing that at 60FPS with the resolution turned up was a revelation. It was a completely different game. And yes, the framerate in that game hurt the gameplay. You can't tell me you didn't find Blighttown to be a near disaster running at or below 30FPS at times with the hostile enemies and environment. It would have been so much more enjoyable to play that section of the game at 60FPS+.
As someone who got to Dark Souls 1 on PC long after the mods, and patches, the frame limit remover actually did change the game. It made it worse, for me. It reduces your weapon durability, it changes the timing for evasion and reduces your invincibility frames, it shortens the length of your roll and jump, and worse by changing the animation and hit detection you get nailed by swings/actions you aren't even in the line of anymore.
I'm glad you mentioned Blighttown because there is a short cut there that requires a jump. I missed the jump 9/10 with 60 FPS, at 30 FPS I nailed it every single time. Same with trying to get up to the bird to get back to the asylum. The expletives I screamed when I'd watch some youtuber "just roll onto the platform" and I'd fall every single time not understanding why.
TL;DR:
DS1 actually benefits more from 30 FPS. At least if you don't want to get frustrated with random deaths at attacks you could have sworn you dodged.
I'd take DS1 30FPS over 60FPS any day. Resolution mod, you got that right. 720p native is HORRENDOUS and DS1 is actually beautiful when not restricted to such a low resolution.
However, to your actual stance - I'd take 60 FPS any day of the week if it doesn't break game mechanics (NFS, I'm looking at you!)
(but now with G-sync, I find 32 FPS more than acceptable haha).