definitely would need to reduce hit points in addition to armor. many quality designs rely on a combination of evasion and hit points for survival as armor is expensive and those things are free. cap or hcap light vehicles are already quite strong among attacking options, and multiplying their survival by a factor of nearly ten for a cost increase of (presumably) 100% would revolutionize ground combat.
despite the elegance of the suggestion, it seems to me that many unintended consequences would be avoided at a small cost in effort if the more prosaic approach of simply defining one or a few "aerospace" unit types were taken instead.