This is kind of a slippery slope. How many of you were around during the days of Super-Bro? They had to nerf his shields because he was capable of timing out entire teams by himself. Druid was essentially the only thing you could use against him and even then it was tricky.
Also, if we see an increase in livability from tanks, how is that going to affect the DPS class, so on, so forth? For every argument for an upward motion on one thing, there is another argument for equilibrium or even limiting those capabilities.
I think a lot of the improvements that people want can be achieved with runes - that's kind of their function. They're limited, so you have to choose which stats you want wisely. It adds an element of challenge to it. There is no such thing as a "perfect" hero, they all have flaws.