Rambling because I want to put the thoughts down somewhere and these are thoughts that will probably be disproven the second I look back at the genshin wiki but WHATEVER, I'm having a thought -
Something about the idea of visions putting an elemental stream inside of their wielders or a way for them to connect with the elemental flow of the world around them...like yes, I know the visions are physical manifestations of their holder's ambitions and dreams, but it's never really addressed how this actually works. We know if someone's vision is taken away or destroyed, it's like a physical part of them is also removed/destroyed. We also know that when a vision holder dies, their vision also fades. It can be understood then that visions are more like conduits for their holders to connect with an elemental stream and channel elemental abilities.
But that doesn't explain *where* the elemental energy is coming from.
I like to think all beings - human or otherwise - are able to connect to the elemental energy flowing throughout Teyvat, but there's a difference in having the ability to do so versus gaining the means to do so. Beings that are native to Teyvat - which are, without going into extreme detail, literally all elemental beings and creatures except humans - are inherently in tune with the waves of elemental energy that makes up their world. It's why they don't need visions to use elemental abilities. Think of creatures like slimes, regisvines, vishaps, etc.
Humans on the other hand can gain the ability to tap into this greater pool of elemental energy, but aren't inherently able to connect to it from birth. But just like each elemental being has a specific element that they can connect to, visions grant humans the ability to connect to one specific elemental stream of energy - which is why you have seven different vision types. When a human is given a vision, it's also like a door is opened or a pipe is unclogged and allows the elemental stream to pour inside of them. When they use their elemental abilities, the pool empties and has to take a short amount of time to refill - such is the same with native creatures of Teyvat on a similar but different scale (see pyro slimes that go out for a bit vs a pyro user having to wait a recovery period before using their elemental skill again).
Remove someone's vision and you remove their ability to connect to this elemental stream. However, it does not close the door that was already opened - once the vision is returned, the vision holder can resume using it as if it was never lost. Though I also think, unlike elemental creatures that constantly have an inward and outward flow of energy, this can cause a buildup of excess elemental energy that the human body cannot regulate. Overabundance of any form of elemental energy in a human body runs the risk of driving them mad, turning them into a "lesser" elemental being or, potentially even worse, cause them to be reabsorbed into the elemental stream as a whole.
We, of course, have never seen this happen to anyone in game but...idk, it's just something I'm thinking about at the moment and needed to get out of my system for now.