Ah, this is where it gets difficult to explain without a visual aid.For example, you write "it instantly becomes a memory for him in the present". But it wasn't instant. He didn't remember it until years later. It's just that we, the audience, were shown him remember it an instant later. How did the universe decide at what moment he was supposed to remember that?
Remember that Desmond and Daniel started out as contemporaries in the story. Then at some point, Daniel traveled into the past to an earlier part of the timeline, while Desmond continued on from the point of Daniel's departure. Even though he's 30 years in the past, he's still moving linearly through time, just from an earlier starting point.
The interaction Daniel initiated in the 70s was instantly a memory for Desmond in the 2000s. I wonder if this helps to visualize what I'm trying to say:
== 2000s
* flash
---- 1970s
V interaction
^ memory
Daniel ============*-----------------V---->
Desmond ========================^===>
I'm not sure what you're saying. You have the switch to the 1970s after the flash in Faraday's history, yet his interaction with Desmond happened in the 2000s, not the 1970s. What happened is that, in late 2004, the time flashes begin, and Faraday starts bouncing around time with the other losties, while Desmond and several others escape from the Island. Faraday only spends a few days bouncing around time, before ending up in the 70s.
During those few days, one of his time skips takes him to some point in the early 2000s, when Desmond was in the hatch, and they have their interaction. Desmond doesn't remember that interaction until *2007*, several years after he left the Island. Desmond had left the Island several years ago, while Faraday had only experienced Desmond leaving the Island a few days ago. Are you trying to argue that no, they actually experienced the same subjective amount of time since then?