So I have made many many posts on this subject, and I was writing another one when my browser decided that clicking back to the tab meant I wanted to close it and lose all my work. So this post is going to be a little shorter than I originally intended it to be.
The raw material trader is broken. The two other material traders group materials based off of what type of material they are, emissions data, shield frequency, focus crystal, ect. This has two very nice benefits, one it means that the rarity of all mats is respected. All very rares are on the same level, all rares are one level below that, ect. This means that you aren't going to get silly circumstances where a common material is worth more than a rarer one. (unless spawnrates are messed up like with cif and mef, but that's not the fault of the trader) It also benefits from the fact that blueprints tend to respect material types; a blueprint that uses flawed focus crystals for a lower grade will use refined and exquisite for it's higher grades. This has the nice effect of allowing anyone who can afford a high grade roll able to trade that roll for multiple lower grade rolls without having to worry about the category conversion penalty.
The raw material trader doesn't have either advantage. It disrespects material rarity to a ridiculous extent and doesn't even try to respect blueprints. Now it's a little understandable why it would do this, as there are no pre-established material categories like there are with manufactured mats and data and there were different numbers of elements of each rarity (the devs seemed to have changed this in the beta though), but the current raw material trader doesn't even try to work around those issues. If we were to take the current raw mat trader and fix the rarity symbols so they reflect the actual rarity of each element according to the game, we would get this:
Crazy, right?
Even worse however, is how blatantly the categories ignore the engineering recipes. I went through every engineering recipe (yes every one. it took a long time) and drew a line from one mat to the next every time I found an element that was replaced by another in a recipe when you went up a grade. This is what it looked like:
The end of an arrow represents the higher grade recipe. Arrows of the same color connected to the same element are from the same recipe, so a red arrow pointing from material a to material b is from the same recipe of a red arrow pointing from mar b to mat c. Arrows that do not connect to the same material are not from the same recipe unless they are chained together by arrows of the same color. Grayscale arrows are from recipes that had more than one element, requiring me to use outside trends to determine which element preceded which.
This graph can tell us 2 things. 1: there is no correlation between the engineering blueprints and the raw material trader. 2: There DO seem to be trends in what material succeeds which, and they tend to be groups of 5 materials containing one material of each grade. This means that it very well is possible to create a raw material trader that respects engineering blueprints AND respects element rarities. Such a material trader would look like this:
As you can see, this version respects rarity much more, never putting a more common material above a rarer material, and only breaks a direct 1 grade increase pattern in the last category and that's only with the new materials which could easily receive a rarity increase to fit in better.
As for how the engineering blueprints work with this trader, take a look, I have drawn arrows representing all of the relationships between mats, with the arrows getting larger the more common a relationship is.
Not perfect, but about as good as you can get.
Please consider implementing this.
The raw material trader is broken. The two other material traders group materials based off of what type of material they are, emissions data, shield frequency, focus crystal, ect. This has two very nice benefits, one it means that the rarity of all mats is respected. All very rares are on the same level, all rares are one level below that, ect. This means that you aren't going to get silly circumstances where a common material is worth more than a rarer one. (unless spawnrates are messed up like with cif and mef, but that's not the fault of the trader) It also benefits from the fact that blueprints tend to respect material types; a blueprint that uses flawed focus crystals for a lower grade will use refined and exquisite for it's higher grades. This has the nice effect of allowing anyone who can afford a high grade roll able to trade that roll for multiple lower grade rolls without having to worry about the category conversion penalty.
The raw material trader doesn't have either advantage. It disrespects material rarity to a ridiculous extent and doesn't even try to respect blueprints. Now it's a little understandable why it would do this, as there are no pre-established material categories like there are with manufactured mats and data and there were different numbers of elements of each rarity (the devs seemed to have changed this in the beta though), but the current raw material trader doesn't even try to work around those issues. If we were to take the current raw mat trader and fix the rarity symbols so they reflect the actual rarity of each element according to the game, we would get this:

Crazy, right?
Even worse however, is how blatantly the categories ignore the engineering recipes. I went through every engineering recipe (yes every one. it took a long time) and drew a line from one mat to the next every time I found an element that was replaced by another in a recipe when you went up a grade. This is what it looked like:

The end of an arrow represents the higher grade recipe. Arrows of the same color connected to the same element are from the same recipe, so a red arrow pointing from material a to material b is from the same recipe of a red arrow pointing from mar b to mat c. Arrows that do not connect to the same material are not from the same recipe unless they are chained together by arrows of the same color. Grayscale arrows are from recipes that had more than one element, requiring me to use outside trends to determine which element preceded which.
This graph can tell us 2 things. 1: there is no correlation between the engineering blueprints and the raw material trader. 2: There DO seem to be trends in what material succeeds which, and they tend to be groups of 5 materials containing one material of each grade. This means that it very well is possible to create a raw material trader that respects engineering blueprints AND respects element rarities. Such a material trader would look like this:

As you can see, this version respects rarity much more, never putting a more common material above a rarer material, and only breaks a direct 1 grade increase pattern in the last category and that's only with the new materials which could easily receive a rarity increase to fit in better.
As for how the engineering blueprints work with this trader, take a look, I have drawn arrows representing all of the relationships between mats, with the arrows getting larger the more common a relationship is.

Not perfect, but about as good as you can get.
Please consider implementing this.