Building off of this from another topic
I feel like theres alot of misconception in general as to what makes a hero a tank and it took a while for the hots team to figure out what a tank even was in hots to.
With how to make a tank, I think how reliable their CC is super important. If the skills got to much counterplay your entire kit falls apart as a tank. Like you mentioned, blaze and yrel are great examples.
On paper, blaze has one of the better stuns on the game but in pratice, that slight start up the move adds a huge level of unreliability to blaze as a tank.
And then yrel has it even worse with with a 2 second delay on her abilities. While she can use her trait to speed things up, she can only do so with 1 ability.
This is gonna sound crazy but I think theres also misconception that teams even need a traditional tank to be well rounded. What a team actually needs are a way to engage, peel, and a front line (granted, good tank kits generaly provide all of these things). For example, a lineup of sonya, imperius and anduin or deathwing, maiev, cassia can make for a still well rounded team.
This is how heroes like arthas and stitches still manage to find viability dispite being bad tanks.
Stitches has good engene. I dont think I need to go in more detail then that.
Arthas has really really peel against a specific kind of hero (melee auto attackers). This is where his niche comes from dispite a kit thats bad at engaging.
Then, Malganis has pretty bad engage and fairly meh peel. His Q is super slow, his E being just a sleep can make it somewhat unreliable as peel in the chaos of a teamfight and both abilities are very telegraphed. Malganis ends up playing more like a bruiser that spams CC instead of having good damage.
I think what makes it so hard to make a proper tank is finding the sweet spot between to much counterplay and not enough and the misconception that its the tanks job to just be hard to kill.