Should Singed with Rod of Ages and Rylais Scepter be tankier than Garen with Randuin and Banshees?

I have played several games with Singed and I'm noticing a trend with him. He is tankier with a beefy ap carry build than a tank building full tankiness. Just with Rod of Ages and Rylai's Scepter Singed can out-tank almost any other tank building items meant for solely tanking. All while building a decent AP damage output. Late game he becomes almost invulnerable to all but a 3v1 or 4/5v1 while doing enough damage to take any melee champs down a good deal (even if they have some MR). Overall I feel like there needs to be more of a seperation of his tanky build and damage build. All other tanks have to choose if they want a semi tanky build with some damage output or if they go full tank and forsake doing damage. I think Singed needs to feel this seperation a bit more. Take back his innate tankiness a little so he isn't on par with a Malphite for survivability, yet able to deal as much damage as some ap carries.