note: this is a work in progress, also a wall of text.
as it is now the crafted weapons minimum level is higher than random loot. it has been stated by the Devs that this isn't what they wanted. after a bit of research, that isn't finished yet, i'm seeing where the problems are. first part of the problem is in the enhancement bonus shards. i've dug around and found that plain weapons with enhancement bonuses have the following minimum levels:
+1 is a 0 minimum level
+2 is a 2 minimum level
+3 is a 4 minimum level
+4 is a 6 minimum level
+5 is a 8 minimum level
so we can conclude that the enhancement bonus is supposed to raise the min level of the weapon by those numbers.
as it is now a crafted weapon with no effects end up raising the min level of a weapon by the following:
+1 is a 1 minimum level, shard is +1, formula is 2 times the + on the shard minus 1
+2 is a 3 minimum level, shard is +2
+3 is a 5 minimum level, shard is +3
+4 is a 7 minimum level, shard is +4
+5 is a 9 minimum level, shard is +5
in each of these cases the minimum level is 1 higher than random weapons. so either the + number of the enhancement shards needs to be lowered by 1 on each or the formula needs to be changed to 2 times the + on the shard minus 2 to match random loot. if the crafted weapons are supposed to be 1 level below random weapons then the + number needs to drop by 2 or the formula needs to be 2 times the + minus 3. lower the + of the shards by one has been suggested in other threads by a few people. i think the + of the shards needs to be dropped by 1 due to the second part of the problem.
i did look around at a lot of weapons on AH this past week, one good thing about crafting being down, there are a lot of weapons on AH now. i have figured out how much a lot, but not all, of the effects raise the minimum level of weapons. i concentrated my research on weapons that cause melee damage and didn't do any for weapons that boost spells. for the most part effect shards with the current formula will be 1 level below random weapons with the following exceptions.
the bane effects, lesser bane, bane and greater bane add 2, 4 and 6 to the min level of a weapon. right now the shard plus on each tier is 1, 2 and 4. the first 2, lesser bane and bane will be 1 level below random while greater bane will be 1 level above random. greater bane needs to be 3.5 to match random weapons. to be 1 lower greater bane needs to be 3.
bone breaking adds 4 to a weapons min level, right now shards have no + so a crafted bone breaker will be 4 below random, this shard should have a +2 to end up 1 level below random.
metalline adds 4 to a weapons min level, right now the shards are +4 which would make these 3 over random. this shard should be +2 to be 1 level below, 2.5 to be the same as random.
impact and keen, both of these effects add 2 to a weapons min level. right now impact shards have no +, keen has a +1, impact needs to be a +1 as well for both of these to be 1 level below random, to be the same they both need to be 2.5.
these are the ones i've found so far. there are still a few more to research plus there are the spell effects for weapons to research. though i did notice that some spell weapon effects can be either a prefix or a suffix, which is a discussion for another time.
for future reference i did find that the following raise the min level of random weapons by 10, disruption, smiting, paralyzing, banishing, and vorpal. so, each of those shards, if and when they are introduced to crafting will need to be +5 to be 1 below, 5.5 to be the same as random.