Just curious

Why do champions have higher damage output when they have

a) mobility out the ass b) no resource gate c) both

I thought I read something about riot wanting champions to pay for mobility and the like... and how if katarina got mana her DAMAGE would be buffed? (katarina is fine, just an example of a champion known for burst damage and how riot sees it)

What is the logic for it other than making fun champs easier/flashier to play? If that's it... does that really fit competitively?