Why HP inflation is a valid concern

[Kitfox]

By adjusting enemy mechanics and their potency for a given skill. Hence why many current tank busters inflict a damage taken debuff to force regular tank swaps (and also why many 270 STR acc wearing tanks get obliterated, because they do not have the expected HP value the attack was balanced around) and those tank busters are generally not going to be aimed at the DPS, who take attacks the tanks can more easily brush off.

Balance is manipulated on more then just the players side of the coin.

Raid AoEs hit everyone, including tanks. If you balance incoming damage to tank hp, non-tank hp gets weaker, or if you balance to non-tank hp, tank hp get weaker. This is why you can't have the stats linked.