Frazetta's was great at that specifically...
Broadly speaking, discipline is obviously a good thing. But turning oneself into a human camera is a great way to sterilize your art. People will be impressed, sure, but they won't care . And that's what ultimately matters, I think. Obviously this doesn't apply to every field. If you're doing conceptual art for Boeing or something, by all means, be as technically precise as possible.
I think that Frazetta's work not necessarily is overall photorealistic - there is an influence of realism, that for sure.
However while a lot of the work is realistically renerded imo the overall proportions used are sometimes much more reminiscent of idealized American Action Comic figures. Even the strong placative style with broadly used black areas and how clearly cut some compositions are underline this impression.
Is his work realistic enough to be believable? I think so
While if you look at Vallejo it's a lot more realistic, much more detailled and a lot more exact - it's also going much more in the direction of photorealism.
Vallejo seems to come from a completely different perspective than Franzetta - there are very fine gradients (Franzetta doesnt have that "quality" at the same level in his works - he just uses simpler gradients and it's also fine) and very realistic proportions and little details (but Vallejo needs exactly those fine gradients for his richness in details)
In terms of subjects and color choice those 2 artists seem to be very similar to me, but if it comes to their technical approaches and value priorities not at all.
And it's also hard to say which style I ultimatively prefer, because both are very nicely balanced in terms of techniques and how they are used.
Fact for pixel art is that it doesn't support fine gradients.
By having limited colors (in whatever form) the quality of any gradient will suffer. Ultimately limited colors cause bands.
There are 2 ways to avoid banding:
-either using tons of colors that the gradients are so smooth that the banding will rather look like a gradient
or
-to use as few colors that you carefully can control the outcome of the banding and shape the cluster edges effectively.
Ultimatively both is possible with pixel art, but making fine gradients is a huge timesink and that's why we see this quality quite rarely in pa. And it's also a lot more efficient and easier to pull this technique off with another medium.
Pixel art further limits one on line quality and placement, which is further bad for realism. Here it might also be much smarter to go in the more expressive direction, just because there the question with a low resolution is rather "do i ifll in the pixel at the left or the pixel at the right" but for very realistic depictions you need subpixels in the middle that everything looks good.
That mindset of me is the outcome of a very long experimenting process where I intentionally tried to break a lot of those limitations.