Thank you for this mentions.
I do believe that Level 4 Features offer more variants, so even naturally more rigid skaters can fulfil criterias. I definitely never want to see a skater being "punished" for his anatomy.
Because body anatomy and flexibility must be taken into account.
Some skaters have naturally more loose ligaments which allows them to be more flexible. Doing flexility exercises since childhood helps a lot in loosing ligaments as well. Many skaters are hypermobile in one or more joints and loose ligaments play smaller part in it.
But not everybody is hypermobile.
Joint's anatomy is essential coming to range of motion. Some people have joint anatomy which decreases range of motion in some directions. You cannot do anything with it despite how much or long you practise.
And if you try to get into the position which your joint is not build for - you always use wrong movement stereotypes overloading other body segments...which will lead to injury sooner or later.
I remember Miki Ando being criticized A LOT by American commentators (Dick Button, Peggy Flemming?...I am not sure). They didn't like her low flexibility especially in Spiral Sequence. From my medical view, I am almost sure that Miki has hip joint anatomy with reduced range of motion into hip extension (leg behind) and external rotation. So for her it was impossible to get proper position on classical spiral with leg behind or in Bielmann position. Some commentators never forgot to mention it, not thinking even for one second how strange it is that workoholic Japanese lady who is doing flexibility exercises for years (like everybody in figure skating) has so small range of motion in one direction.
Another part are shortened muscles or fascias or myofascial lines which decrease range of motion, it is another reason to have regular Rehabilitation treatment. I am surprised how many elite skaters are fighting with it (as it is visible even when they simply stand on the ice). I do understand that Figure Skating is expensive, but proper Rehabilitation is injury saving or injury postponing thing...it really does have sense.