A 1/1 for 2R doesn’t sound all too hot (pardon the pun), but having a tap ability that deals 1 damage to target creature or player is an extremely powerful effect in a Limited environment. In ordinary Constructed, a 1/1 is easily dealt with, but in Limited where removal is much more precious, a little 1/1 that can tap each turn to do a little damage is annoying but not enough most of the time to use a removal spell on. Pyromancer can give you incremental value, which is a very important thing in Magic. Truthfully, though, once he was bumped up to uncommon, he wasn’t quite as good anymore.
Although, you can still play him in a Pauper environment, since he was in fact a common at one point, Prodigal Pyromancer just isn’t strong enough in that environment due to the many 1 and 2 damage instant removal spells that exist today (not to mention Shock and Lightning Bolt which have been around forever). However, there are some interesting interactions that can be made with the Pyromancer that can be relevant in Commander. Were you to give him an equipment or Enchant Creature card that gave him deathtouch, that 1 damage would be lethal to any creature it’s dealt to, since it’s damage being dealt by a creature with deathtouch. This is true of lifelink, as well. So there are definitely ways to extract even more value out of this guy.
All in all, he’s still a fun little card, especially in Pauper Cube, an increasingly popular format where you use only one copy of each of the best commons in any given color and draft them. He’s a little weak for other Constructed formats, including Commander, but he’s still one of the better commons in the game as a Red 3-drop.
You also have to love that flavor text: “Learn to Burn!”