Of course it's a myth.
After all, the idea of "perfect form" is just that - an idea. It's not actually something that exists. How could it? It's a concept of reality, which means that by its very nature it exists only in your mind.
First, we should ask: why are we trying to define perfect form?
I suspect this comes from beliefs that suggest our world is entirely knowable: with time and the right tools, we can understand any system to optimize its function. Then we'll know how to make it work perfectly.
It's the same type of thinking that asks questions like "what's the best workout program?" or "what's the best diet?".
Over the past century this type of thinking has been discarded by nearly every major branch of science and philosophy - perhaps seen as an ideal goal, but not something that's actually possible in the majority of cases.
Especially in biology, any statement that uses "optimal", "universal", or "perfect" has no place whatsoever unless it's understood to be meant as "the best we can ascertain based on what we know" or "pretty good for most populations".
We're strong at making "better" or "worse" statements with decent accuracy, but even those statements can't be mapped onto all cases. Even if we could know what "perfect form" is, it certainly couldn't be applied to everyone as there's tremendous variability between individuals (even in statistically similar populations).
Take bone lengths, for example. In a population there are average lengths for each bone in relation to your height. However, bone lengths may differ by a few percent - and that can make a big difference.
As an example, the femur is about 24% the height of the body and the trunk about 29.5%. How long your femurs are in relation to your trunk will change your squat pattern: that's why people with shorter femurs and longer torsos will always be able to stay upright in a squat and be strong at the bottom.
Those of us with longer femurs and shorter torsos will have to lean further forward to hit the bottom position of a squat and will generally be weaker in that position.
Likewise, a smaller wingspan, lighter bodyweight, and shorter legs and will substantially reduce force demands in leverage-based movements like the iron cross, front lever, and planche.
"Optimal" becomes less useful as individual variations creep into the equation.
There are also other anatomical variations to consider. Some people have hip sockets that prevent them from squatting below parallel with a close stance, but they can hit the bottom in a wide stance. Others can practically sit on their ankles when their feet are placed together, but can barely hit parallel if they're wider than shoulder width.
Factors like depth of the hip socket, muscle insertion points, the angle and rotation of the femurs all influence what types of squat are most optimal for which lifter.
Likewise, one can perform an iron cross in two different ways - with internally rotated or neutral shoulders. The former has the advantage of increased stability, but it's uncomfortable and unnatural for some athletes. And, if you're more lat dominant (and with strong elbows), you're probably better off working with neutral shoulders for an iron cross. You'll have less initial stability to work with, but likely faster progress in the long run.
Finally, there are specific goals. If you're a powerlifter, it makes sense to squat with a slightly wider stance to utilize the hips and stretch reflex. Your goal is to lift the most weight possible, after all.
Likewise, if you're an olympic weightlifter, you're probably going to go with a form that allows you to squat deep, in a close stance, with an upright body position. After all, you need to squat like that in order to receive a heavy clean or snatch during competition.
Thus, it's also important to ask why one is doing a certain exercise; "perfect" must be placed in the context of what one was trying to accomplish by using that specific form, as different techniques are more or less adequate for different purposes.
Instead of chasing the myth of "perfect form", focus on "better form".
Instead of chasing the myth of "optimal technique", focus on teaching yourself to problem solve, troubleshoot, and learn your own body.