Poor, common, uncommon, rare, epic, legendary I think is how it goes. Common is gray, and depending on the level of the node/animal I think u will get a diff chance of mat, exe. lev 10 node will only give you legendary mats, and will also give u a higher chance of epic, and rare and so on.
Could be totally wrong but pretty sure critical harvest is when u get stuff during the.... harvesting, like first boom 2 ore and 1 essence, second boom something els so on. Weak points during the harvest (the + signs) just speed things up and give you a dmg boost for the hit, don't think its affects mats. "Drops that pop up while harvesting are the critical part".
Beneficial (possibly Plentiful too) harvest is just for the last hit, I usually get higher tier mats and more lower tier from the BH.
I just did my first uncommon weapon the other day and was very disappointed. So... turns out that there IS a diff in dmg and stats when crafting a item from poor to common, but after that you will craft the same item regardless mat tier. The only diff in mat tier is that u will get 1 more experimentation MAX point per tier.... so lets say a common item gives you 7 max points that u can put into the experiment, (just guessing the number 7) the only diff a uncommon will give is that u can put 8 total points into one category. When your skill in blacksmithing is really high you "CAN" craft very good items, but until then u can make comparable items from crafting stuff from common mats, just make a lot of them and separate the amazing, great so on, from the garbage ones.
"You can save all the legendary mats u get and make a item, and then fail the crafting experiments and get something worse than your common one".
just throwing that out there, might be off a bit, lemme no if I am =)