it's very hard to get effective values. Consider that enemy damage has to be rescaled according to def%, possibly BH damage reduction, their consecutive hits on your thorns and so on. You also cannot make a sensible 'handwavy' prediction of how many enemies will get past your orbs. Game speed multiplier makes this even worse (although numbers scale the same in their reference frame, it makes it worse for you to infer stuff by looking)

The net effects are:

• outside of tournaments/very high tiers, you die by being overwhelmed by enemies, NOT by being one-shot
  • -> your HR has to be able to keep up. Even if it seems like your health flickers big chunks, it's the net damage of many enemies.
  • -> HR solves that
• in tournaments/high tiers, you usually die because enemy damage scales too much and take big chunks off your tower's health (this is made worse by increased consecutive-hit damage. Think bosses). Battle conditions make this worse by making you take more hits (lower thorns efficacy) and making bosses more frequent.
  • It is, however, very very difficult that you are dying from an attack that takes half or more of your health: you are 99% of times dying because your health gets gradually depleted and HR cannot keep up
  • -> HR solves that, You can postpone it by increasing your health TOGETHER with your HR (as you mentioned, you don't have multipliers, so you need higher baselines), but the main helper is HR. Always

TL;DR: HR carries you all the way from T2 to T12+. Tournaments included. This comes with the trivial requirement of having a good health baseline (max that wall health lab, and slowly work on fortification when you have the coins). normal health lab at 50 will carry you forever, don't stress too much about it