I don't think a lot of people realize how good tanks can be. It's just that some tanks don't deliver enough constant cc (or other relevant utility). Sejuani for example is pretty much a walking ult. If she didn't have ult and she goes in with Q, woopdy doo. Her slow isn't that great, and her damage isn't that great from that point on either. Only the squishiest/underleveled target with no equal amount of items should worry about her jumping on them.
But on the bright side, I can pick mumu, Malp, Naut, etc. and buy things like sunfire, iceborn gauntlet and thornmail to deal incredible sustained damage and not die when everyone focuses me that instant. There should be better MR items for tanks that aren't purely selfish defense (BV and SV are great if you buy them back to back, but don't help you 1v1 APs like the previously mentioned armor items can help you 1v1 ADs). Iceborn Gauntlet is just a superb item at the moment. I finally feel like I can stop Rengar from snowballing when I can build a damage-dealing-defender.
Again, TANKS need better MR items - or Riot will maybe introduce a line of AP Bruiser items like that reworked Abyssal Scepter from not long ago. We don't need to have 30 second fights from champs being too tanky, and in the end, the victor of a fight should come down to the most skilled and intelligent player(s).