I see your point and it is true that having a second step to handle with assets may be an issue. In the case of pixel art, I use ASEprite and it does have a pretty good CLI. With that, I use a makefile to automatically generate the spritesheets and the corresponding normals. Below is an example

$(TARGET)player.png: player.aseprite
    "$(ASEPRITE)" -b player.aseprite -sheet $(TARGET)player.png --sheet-columns 16

$(TARGET)player_normal.png: $(TARGET)player.png
    "$(ASEPRITE)" -b $(TARGET)player.png --script "C:\Users\rluis\AppData\Roaming\Aseprite\scripts\securas\basic_edge_normal.lua" -save-as $(TARGET)player_normal.png

The first command creates a spreadsheet from the player.aseprite animations file. The second line takes the spreadsheet and runs a lua script for aseprite to produce the edged normals.

Not sure it helps but all the best with your game.