Why are you so surprised that tanks die in 5 seconds, when team fights can last 5 seconds? If tanks do die, then they did their job being focused down, compared to the carries that they protect and peel. That’s the point of most tanks: to be focused down by the opposite team while the tank’s carries and teammates kill the other team.
Plus, abilities matter in terms of tanking. Braum’s fuckyoushield is an amazing defensive weapon and his ultimate is a team fighting game changer if done right. Kalista’s passive will only get you so far, plus she has much lower range compared to other ADCs so she needs the HP. Lastly, Braum is supposed to PROTECT OTHERS, AKA take and intercept ALL DAMAGE that would be aimed at carries and bring it to himself. AKA, very valid reason that he dieS faster, knowing that he did his job right.
Looking at this thread of yours makes me want to question the legitimacy of your idea of balance (maybe you just need to git gud).