In competitive play, those abilities aren't helpful.
Starters (that have Torrent, Overgrow, or Blaze) generally get outclassed by starters with their hidden abilities. This is because the hidden abilities are so much better.
For example, Typhlosion has the Hidden Ability Flash Fire. This means that it can switch into a Fire-type attack and deal massive damage (with a Fire-type move) when combined with Charcoal. On the other hand, Typhlosion with Blaze wouldn't be very helpful because, like what you said, the 1/3 health is hard to get and is risky. Opponents can just 2HKO or OHKO that Pokemon with coverage or STAB moves and the ability (in this case) Blaze would never activate.
Of course, there are some exceptions, like Torterra and Samurott. In this case, Overgrow / Torrent would be more helpful than Shell Armor.
Hope I helped!