I hated that they made it a "regular" magic type in the later games, scaled with your stats. It was a great support magic for melee builds, afterwards it just became another casting build.
The change I feel is mostly for balance. Since PvP only cared about your level pyromancies were freat for twinking. Also you didn't really have a way to gate how strong a pyromancer could be at any point of the game since the flame required souls and nothing else to upgrade.
yeah except of course that dark souls 2 pvp didn't care about levels but instead soul memory and the change from pyromancy to "just another school of magic" happened in dark souls 2, making the decision a completely nonsensical one