Searing Blood only deals 2 damage to a target creature, and the 3 damage to the creature’s controller only happens if that creature dies that turn. Searing Blaze only deals 1 damage to a creature and its controller unless you played a land that turn. The Dragon-centric requirement for Dragon Roar is in many ways more limiting, but it’s stronger overall if you do have a Dragon to satisfy it.
This is very playable depending on the Dragons you run. A lot of Constructed red decks play dragons, such as Stormbreath Dragon in Standard and Thundermaw Hellkite in Modern. That being said, I can Dragon Roar working pretty well as at least a sideboard option against creature heavy decks, as long as Dragons are on the menu.