Why HP inflation is a valid concern

[Kitfox]

I'm sorry, how does this explain why having our attack power scale at a fraction of our VIT is a problem?

The AP scaling factor is something that affects the entire level range, it doesn't change based on level. Some scale that works with gear at lvl70 might not work at lvl30 or 50. Changing the scaling factor has a chance to break something elsewhere. Changing VIT and STR on new gear only affects new fights and they can be tuned without affecting prior gear and scaling. Separating VIT from AP also doesn't affect incoming damage or non-tank VIT values when they want to tune tank dps, so it's better for balancing.