I would actually advise against Eruption in-game. In-game, you aren't always going to be at full health, as damage accumulates as you play. Also, frequently there is only one Pokemon you need to take out, and Blast Burn serves as a powerful finishing blow to the opponent.
Once you're post-game, slap a choice Scarf on that Typhlosion, and spm Eruption for al you're worth.