First of all, I was talking about the passage of the game from Tamora onwards, so your example of fight with a lurker in the early game does not apply. Now, if you look at the statistics posted by Hedin from the end of Tamora, his character has 56 defense and 364 life. The vast majority of mobs in Tamora have 140 strength, which means that a character with 56 defense will sustain 84 damage per hit, which means that his character can take 4 hits and a fifth hit will kill him. But a character who invested everything in protection gear (shield, belt, jewellery, helmet) can reach in Tamora 134 defense on legendary. That means he will take only 6 damage per hit, so at 364 life he can take 60 hits before he dies. So, juding by your own logic, that "what is important is how many hits you can survive" , which one is the better ?
Regarding these particular stats - Hedin has quite a bit of health due to SNK being a bit imbalanced (in my opinion) and afaik it is a first run with these settings, so we'll have to wait and see how it changes

Because of this amount of health, HP jewellery is irrelevant, and in the case you are talking about, full protection will of course make you tanky. The question is whether it is worth trading off that much damage, and that would depend a lot on your playstyle preferences.
Personally, on Tamora, I would upgrade armour (to make belts, but +20 defence comes as a bonus) and take a helmet - that would be 68 armour, but then the rest I would put in primary stat, which is +30 with amulet, +10 for rings (or more, depending on str/dex choice) and +10 with belt. With skill being around 60-70%, that is 30-35 average damage per hit.
So I'd say against strong mobs with high damage and high defence, the primary stat takes priority (but only if your damage is above defence ofc). Cleaning up wolves, etc which die from 1-2 hits either way - defence is better.
And if you are playing ranged, then the primary stat is even more important.
But either way, you can also swap in between. One does not exclude the other if you have enough resources.