Actually, you are mixing up some things
Most important thing is the area level (they aren't used in normal, but nobody cares about normal anyway).
The area level determines the monster level (mlvl); champions get a +2 bonus, bosses and their minions get a +3 bonus. Act bosses have their own mlvls; don't know about superuniques/quest bosses.
The item level (ilvl) is set to the mlvl of the monster dropping it --- it's not a property of the item, just an indication of who dropped a particular piece.
In order to drop an item, the monster has to go through a number of requirements:
It must be able to drop the base item (such as "breastplate"). This is where TCs come into play which I don't know a lot about, so I'll skip the level requirements here.
If a monster decides to drop an item, and has selected the base item, it will then determine the quality of the item (cracked, normal, superior, magic, rare, set, unique). For magic and rare items, affixes are rolled based on the ilvl (which is the same as the mlvl, described above), some obscure property of the base item, and the affix level of the available affixes.
If the quality is set or unique, things are simple: every set and unique item has another quality level (qlvl). In order for a monster to be able to drop that set or unique item, the ilvl has to be at least the qlvl.
As a made-up example: suppose a monster can drop a breastplate, and decides to do so. Suppose it wants to drop set quality as well. So it will come up with the Isenhart armor. Suppose that the Isenhart Armor has a qlvl of 20 --- if the monster is only mlvl 19, then it cannot drop Isenhart armors, even if it can drop breastplates.
I believe the Windforce has qlvl 87 (highest in the game). As such, only monsters with mlvl 87 or higher can drop it. I believe all these monsters can drop the hydra bow (base item) as well, so that won't be a problem.
The level requirement has nothing to do with the drop process; it's simply a value in the item/affix database, in "foo-bow has +3 damage, 20 lightning damage, level requirement 23".