I agree with everything that has been said about practice. That was the main reason for me to share "my" view on these things, to point out(by fishing for re-assurance (sorry)) how I think the effect of the described condition on ones ability to do visual crafting is probably minimal (or there even is no effect on it at all, at least none that would be causing "art problems" that are not shared by everyone in the field equally).
And yet, even with the ability to imagine things lifelike like that, I do not possess the skill to just easily recreate the vision into something tangible on a piece of paper or another medium for others to observe.
Does it differ from you ability to capture an actually seen image (life drawing, reproducing a photo)?
Yes it differs greatly from that. Drawing from life or from a photo I find relatively easy once the mind is ready to "see" things in a certain mode. It's exhausting and tedious still and time passes without noticing while in that mode (drawing from life or photo) and the result is never 100% accurate like a camera could capture it (nor do I find that to be a goal worth pursuing as it would just be a waste of time and a camera would do a better job).
Envisioning things like they are there is also different from seeing/observing what is really there. Drawing something "seen" is relatively effortless if I managed to make up the mind that it is what I want to do (judging the accuracy of the result is a different story).
Perhaps envisioning things is equally hard to describe as describing Aphantasia. It is not to be imagined like the envisioned thing is really really "there". It does NOT in part replace the actual perceptual sensation. I still just "see" what's really there, the envisioned image does not override the sensory input, meaning, if it was possible to display the sensory input on some device during the deliberate envisioning of the Dinosaur in the field, the sensory input would still only show the field and no Dinosaur in there anywhere.
Envisioning takes effort and intent. Lots of it. Seeing on the other hand does not, seeing just happens automatically. Dinosaurs (using that as general placeholder for anything) don't just randomly pop in without intent and effort and like just written, the envisioned thing does not replace the visual sensation at all, so if I look and see, there is still just the field, the earth, the grass, some rocks, but yet, the Dinosaur can still be envisioned there. It exists in some place else though, outside of the raw vision and somehow the mind combines both and it's there without being "there". Perhaps that is what I mean by there being the possibility that it is somehow just the mind fooling itself.
What might be an interesting experiment would be to try envision a thing and then try to keep the vision up and running (which I imagine to require insane amounts of intent and effort or "make believe", perhaps even self-hypnosis if that exists) and then on top of that try to draw it like drawing something from life as if it existed not just inside some unknown space in the mind.
Also, now I am more curious about this and would like to know if there are people who can actually envision things in a way that the things really do override the sensory input, e.g. look at your keyboard and "see" a little Kobold there, really replacing the image of the keyboard in parts, like it covers the entire numberpad maybe and hides that from your vision instead of just existing there somehow in addition to the keyboard but purely as a figment of imagination in the mind and you still see the numberpad or spacebar or wherever you imagine the Kobold to be.