Thing is Skarner is good on paper, but if you are able to walk into their team without getting kited and CC'd to living hell then props to you. I play a lot of Skarner, but i stopped playing him mainly because he is a jack of all trades , but lacks in all fields. Rammus is tankier, Jarvan IV has more damage ( can be tankier than Skarner too) and other champs are just all around better.
Again you have to run up to the opponent to do damage. With the amount of mobility in this game you are way better building full tank w/ iceborn and peeling for your team being a utility tank. I used to build triforce elder lizard on Skarner unfortunately that lead to him dying in 2 seconds.