>>24722363HP is a balance mechanism against other qualities like Ability strength and cheapness of attacks.
I think there should be fragile, normal and bulky Pokemon. Pokemon with strong aura Abilities or cheap attacks, or that are basically just played to evolve, should be fragile, and those with only expensive attacks should be bulky.
Example: This Onix is too tanky for how Energy-efficient its attacks are. Imagine it fighting this
>>24722349 Evolution line. If Onix gets to 3 Energy first, or gets a hit in first, it deals 20, then 60, and wins. If Wigglytuff gets there first, Wigglytuff wins. So either Onix is overtuned or Wigglytuff is undertuned.