The code for numbers scaling is already finished. For a regular damage ability, it looks something like…
450x + 5.6sp
…where x is the skill’s level and sp stands for Skill Power. The hard way to fix it is to tinker with the numbers and see what the final math looks like, and the easy way is to just copy numbers from an existing recent hero.
For a team that does this stuff all day long, this kind of basic numbers/scaling pass would take probably 5-10 minutes per hero, tops.