Oh, so your questions are rhetorical. Sorry, that wasn’t clear to me. I re-read your OP in that light, and it seems you don't like how the mechanics treat the situations about which you asked.
Seeking analysis of the proposed changes, not solely a recital of the RAW. Perhaps that needed to be clearer. Yes, in play at the table I found the mechanics wanting. Particularly around movement when blind.
The advantage gained by unseen attackers derives from being unable to anticipate the timing and angle of their attacks due to not being able to see them. It has nothing to do with whether or not their location is known -- they get the advantage whether they are hidden or not -- so there seems to be a disconnect between the reasoning behind the mechanic and your proposed changes to it. For example, an unseen and un-hidden target's location is known. It doesn't need to be guessed by the attacker. Likewise, an unseen and un-hidden attacker's location is known, so it can't be given away.
I agree that per RAW giving away your location does not end your being unseen, and accordingly, you could continue to get advantage. What I found in play is that on larger maps in pitch darkness, numerous instances came up where a creature could attack - giving away its location - but continue to be unseen due to its target's inferior vision. This was subsequently spammed by players: revealing not simply a clever strategy, but a weakness in the underlying rules. The vision rules seem as weak in 5th edition as in every other edition of D&D! Or maybe moreso, due to streamlining efforts. I decided that advantage on the first attack was strong enough to be worth working for without warping the narrative around it. Especially with the out of shifting position.
Looking at that again critically, it could be better to say that advantage is only gained while location is unknown. The only issue with that is then a creature needs to be unseen and unheard, and Invisibility or attacking against a Blinded opponent that you can see would strictly speaking fail to give the expected advantage.
I think this does a good job of elaborating on the rules and could help clear up misconceptions. My personal formulation is that you need to be heavily obscured or behind an obstruction, and that you can't hide from someone who knows where you are.
I wanted to do something like the latter part, but p177 "
An invisible creature can't be seen, so it can always try to hide". "
Always" is strong wording, so that made me feel that circumstances should be able to exist where your position is known, but you can still try to hide. Still, what you say helps me see that what I'm doing is stopping further hiding under circumstances that could well stop the first attempt. Making it inexplicable what is special about that attempt from earlier ones where your position was known. That needs reconciling.
This seems to go against what you wrote under "Unseen but not Unheard". By blind, I assume you mean blinded and that this is meant to replace the Blinded condition. If so, does that mean the blinded creature attacks a target that can see it without disadvantage? I'd assume that isn't what you want either.
Replaces the second bullet, and adds a third. The blinded creature will attack with disadvantage against a creature that can see it, I do not see how what I've constructed obviates that. It deals specifically with the case where all sides are blinded, which can happen under magical darkness or in pitch black underground. Circumstances that can come up frequently in a dungeon or Underdark adventure.
As for movement, I think it's helpful in avoiding the type of interruption to your narrative that you've described to remember that darkness isn't just total darkness. It also covers moonlit nights with anything but the most brilliant full moon. I don't think the range of lighting conditions that falls under "darkness" really justifies a mechanical impediment to movement.
This came out of numerous cases of running through magical darkness, as well as pitch black underground. I would rather say that a moonlit night was dim light, than treat all darkness without reservation as not pitch.