Going over this whole thread it basically looks like the answer is: Bring a retuned deathfire gasp back, add a few more magic penetration items. Game balanced

I dont see tank stacking alot, but it can be frustrating. If you see that becoming a problem have your ranged or melee DPS stack bloodrazors ASAP. I watched a Trist with 2 BR's drop a 4000+ HP chogath in about 8 seconds - solo.

Also, if you see the potential for health stackers I would push harder early... Like a carry, health stacking takes time and pushing towers will slow them down and break them up.

Just got out of a game as tryndamere vs cho'gath and a fed malphite. With my madreds and last whisper i killed them faster than the casters, they were definitetly scared of me. I know it was pretty late game to have all those items, but the complaint is about lategame tanks right?

The single target tanks aren't too bad. It's the ones with AoE that are hell to deal with.
By definition, tanks will have CC--and lots of it. It's their job to punch through the line and make life hard for other people, after all.
The problem becomes that when you're up against 3 or 4 tanks, they can keep you disabled for a long time.
The main problem is that every char's ult in this game does roughly the same damage. Some is more front load, some more bursty--but ultimately they deal roughly the same damage.
So if multiple tanks can keep you CC'ed for 12 seconds, and their ult still work as well as DPS's ult, then they become overpowered.
I have survived some ult bombs before as Soraka (Wish + summoner heal + lots of MR)--they have a really hard time hurting me after that. Of course by that time it's 1v4, and they eventually took me down. Keyword is eventually--their damage really dropped after that first ult bomb. The problem is that generally, you won't live until then.