I play Blaze as a main tank very often in QM, and some times in SL. One of the reasons people feel he is weak is that they play him like a melee tank, similar to JoJo or Muradin, when his real strengths are in his ranged play and zoning, similar to Garrosh. After level 13, and he gets his main damage mitigation tools, you can start to play him a lot more aggressively.
You rarely want to use his E to engage, at least until level 16 and you can talent for the extra armor and CDR. In the early game, use it to escape, peel, or punish divers. Since his E is highly telegraphed, if you have to use it to engage, do so from a shorter range. The area in which the stun applies is larger than most people expect, so use that to your advantage. You can often catch their healer and more aggressive assassins in a single stun.
His W is his bread and butter for tanking. DO NOT LIGHT IT IMMEDIATELY! GRAH! This is probably the most common mistake people tanking on Blaze make. The slow is the most valuable part of his kit when it comes to setting up fights, controlling an area, and creating space for his assassins to do their job. Yes, you can talent for the slow when oil is ignited, and I will take that talent in some matches, but it is a bad habit to get into. I have his W set to On Release so I have the most accurate control of where it goes.
While his self-heal and trait talents are tempting, I much prefer taking his damage mitigation tools. Self-heals can keep you in the fight longer, damage mitigation protects your entire team. Tanking is all about keeping your team in the fight, not just yourself.
Here is my typical main tank build on him, with a few talents that I swap around depending on map and comps:
Level 1) New Habits. I almost always take this one, because it is very easy to complete, Unstoppable on a tank is invaluable, and just the CDR on your trait from globes is worth it. Every now and then I will pick Neural Stimpack, but New Habits is my preferred pick.
Level 4) Oil Dispersal. More oil equals more area control equals more “the enemy has to meet me on my terms”. On the rare occasions I will be picking Grill and Kill, I will go with Adhesive Petroleum, as they have nice synergy, but that is fairly rare.
Level 7) Crossfire. Since Q pierces by default, and reduces the CD on your trait, you should be hitting as many enemies as possible every time you Q. Doing extra damage to them is a solid bonus, and dead enemies can’t kill you. I can’t tell you how many times I have gotten a kill on a fleeing hero because they underestimate the range and damage on Q. I will pick Grill and Kill if they have something like a Samuro, so I can finish the quest quickly. Never pick G&K if they are mostly ranged. I may also pick G&K if there is going to be a lot of very grouped up fighting. That is very rare, though. If you do go G&K, I recommend Adhesive Petroleum at 4.
Level 10) If you are the main tank, Bunker is always a solid choice, especially against something like a Last Rites Malthael. Although Combustion can be very powerful with a good wombo team, until level 20, it is way too easy for the enemy team to avoid unless you are chaining it with other CDs. The movespeed buff definitely did not help Combustion. At all.
Level 13) All three talents are good picks. I will always take Suppressive Fire if their main damage source is a mage, or other ability based heroes. If the enemy Li Ming is silly enough to go Disintegrate, Suppressive Fire shuts her down. It is really good against heroes like KTZ, Orphea, and Q build Valla. If they rely on AAs, go Nanomachine Coating. Remember, you only have to touch the AA hero with the oil to get the attack speed slow. It does not have to be on fire, and they don’t have to stay in it. W has a long enough range, you should be able to make their Zul’jin or Raynor miserable. If you are going Nanomachine Coating, always take Oil Dispersal at 4. Twin Blades Varian? It is to laugh. If I went Adhesive Petroleum/Grill and Kill, I usually take Fuel Leak. Otherwise, go for one of the other two.
Level 16) Thermal Protection. Always. You are a tank, so the extra armor and CDR on your engage/escape/peel is fantastic. In a big team fight, you can often get 3-5 man hits, so have a ton of armor, and your E always available. You can play incredibly aggressively with this talent.
Level 20) Generally I take the ult upgrade. Burn Notice is more of a win-more talent, in my opinion.
Hope this helps!