From what I've seen in my lifetime of HoN, tanks are not as important as people make it seem. Sure, at first, I always had this mindset of having 2 agi, 2 int, and 1 str hero, the str hero being tank, ints being cc, and agis being hard carries. Then of course you start watching high-end games, and you realise, that actually, 3 ints, 1 agi and 1 str can do the job. The str isn't always necessarily a tank, as such, just an initiator. In fact, in most cases, it is. And the int heroes might not just be used for cc, but actually dishing out large dps too.
But for your question: absorbing damage isn't nearly as necessary as proper initiation with someone like magmus or behemoth, as well as co-ordinating stuns and nukes properly, in order to make everybody dead.