Stamina gearing doesn't have to be all or nothing. You should also look at the budget on items. For example, on trinkets you usually get 50% more stamina than secondary stats if both items have the same ilvl. Gems on the other hand have 33% more secondary stats than stamina.
If you are using stamina trinkets, then the difference between gemming for stamina or secondary stats is not that big, certainly not 100k health.
It's not the amount of Stamina compared to secondary stats that matters. It's the amount of Health you gain compared to the avoidance you gain from the secondary stats. The stats behave in completely different ways, and Stamina simply increases your health more than Dodge and Parry increase your avoidance (percentually). That 100k health increase was based on my personal in-game experience when I switched my non-Stamina gems and two trinkets to almost pure Stamina at ilvl 470 or so (counting the bonus from one profession, and the other profession will increase it even further), so I know it to be a legit example.
An analogue to what you're saying could be something like "pizza can't be better than potatoes because you can get 33% more potatoes at the same price". It's not only about the quantity of the stat, but also its quality.
The real issue is finding out whether or not 20% more health is actually better than 8% more avoidance (note that I'm talking about percentages of increase, not actual percent points of avoidance). I'm pretty sure it is, but I don't have any hard evidence yet.