LOVE the fact you went to LXX in Isa. Just the kind of thing I do every day. Excellent!
My point primary point is that the word never meant "cross" as in an actual X shaped piece of wood, which is the way it translated. I point out this as a mistranslation because it is such a simple and, I thought, an unremarkable illustration of how a word meaning "stake" gets turned into "cross" by tradition. My central point is that stauros doesn't mean "cross" and never did. Translating it that way misleads people and causes them to see Jesus's statements in a way they could not have been heard at the time.
But I let me deal with your specific objection. Does the "stake" in Isa 54:2 mean the center support of the tent, the pole driven in the ground, or does it refer to the "pin" that holds down the edges? The Hebrew יָתֵד (yathed) means the "pin" or "nail", not the "stake" that I am referring to. Again, this is confusing because, in English, we use a "stake" to mean these "pins" as well as poles or posts driven in the ground. I am referring to the central support, driven in the ground, holding the cloth up from the ground. As a piece of wood, driven into the ground, what would a Koine speaker call it? I know of no other word, but perhaps I am wrong.
I wish I had never mentioned "tent stakes" because I clearly made this more confusing for you. I know that nomadic people who use simple tents when traveling have with one central pole that is used as a walking stick when moving, You can see this among the Masi today. In my mind, this concept flowed naturally from the idea of following someone, especially in ancient where so many lived as nomads, shepherds, and traveled the crossroads However, forget the tent and the tent pole. Tents are really unimportant to the basic idea which is so universal that it is captured in English as well as Greek.
You are also quite right that I am using the English phrase "pulling up stakes" but only to communicate to the general idea intended by Jesus. The genesis of this English phrase could be tent stakes or the "stakes" we use in mark the boundaries of land, a mining claim or a land claim during the land rush. A very different source idea, but one that also involved "stakes" as poles driven into the ground to establish a residence. This is the universal concept Christ is teaching us about.
It is not the English phrase but the Greek language that creates the connection between "stakes" or "poles" or "posts" and stauros. The Greek word, like the Latin cruces, from which we get "cross", means a piling or pole driven in the ground. The word covers fence posts, foundation posts, and the crucifixion stake. My ONLY point is the fence posts and foundation posts (and tent poles, if the same word was used) were more common that crucifixion posts in people's everyday lives in Christ's era. Only Christian tradition brings the torture stake so strongly to mind. If you do a quick search of word frequency in ancient Greek literature, the use of the word stauros increases ten-fold after Christ, virtually all of it referring to crucifixion. This is perfectly understandable considering the role of the "stake" in Christ's death, but do you see how this just might possibly change our perspective on the word and make it different than what was heard before the crucifixion?
Returning to Greek "stakes" and the English phrase, "pulling up stakes". The general idea of BOTH is similar if not identical. The "stake" sets a place of residences and of ownership, whether it supports a building or creates a fence or marks a claim. In a building, it supports a wall. In a fence or a claim, it defines a boundary. In a foundation, it creates a point of support. In all of these examples, it solidifies an existing established place in the world.
When Jesus talks about "lifting up a stake" he destroying that established position. The word translated as "take up", is airo, which is often used by Jesus to mean "remove" and is frequently translated that way in the Gospels. Notice how badly the meaning of "remove your cross" works and how well "remove a stake" works. It doesn't make any difference if we are talking about destroying the integrity of the wall, the fence, or the boundary. Lifting or removing a stake destroys the establish position, the comfortable place we claim. The use of airo is also problematic with a torture stake since it means both "lifting it" to carry it and "raising it" to plant it in the ground.
The fact that this basic idea of pulling out of an established position works in both English and ancient Greek shows how universal this idea is. It is a deep idea, not one to be taken lightly.
So, we come at last to your statement, "he is talking about discipleship as a loss of one's life." Just go through Mark 8:34, Mark 10:21, Matthew 16:24, Matthew 10:38, Luke 9:23 and related verses and ask yourself, "Is Jesus talking about followers destroying their lives in the sense of dying on a cross or is he talking about destroy our lives in the sense of giving up our established place in the world?" Is he talking about removing the poles that hold us in a place to follow him or lifting up an instrument of torture to carry it to our deaths?
Of course, because I see Jesus as divinely clever, I think he meant both things, at least in a sense, a message for those both before and after his death.
My point is only that to his listeners at the time, the idea that he was saying that the only way they could follow him was picking up an instrument of torture and carrying to their deaths would never have occurred to them.