agree with all your points, having the narrow view of "only this set of mechanics may be covered by items" can reduce creativity. however there is precedent for most items currently in the game existing in dota in some form. Something about the semi permanent nature of mines makes me feel it goes against the spirit of deadlock (particularly in item form, heroes are fair play). Something I think about when imagining new items is their primary function which should be a single thing. What should these mines do. Because a 3k item preventing dashes and doing damage and allowing you to setup ambushes is too many things. Sounds like they should be a farming tool. Then why do they have to be throwable, isn't it better to just have it be a weapon damage scaling farming passive? If they also disable, why will anyone take something like slowing hex? Now we have an aoe disable hex that you can plant in advance. Think about how strong this would be around mid boss. Hope none of this is rude or condescending, just have some time on my hands and browsing all the forum posts I've missed the past few months!
You bring up some valid points, and I will agree that I hadn't considered all of these when I first worked the item up. That said, I don't think the item needs to be reworked from the ground up, mostly just refinement.
RE: Why get Slowing hex when I can get this?
1.) Slowing Hex provides Spirit Lifesteal and is a Spirit item occupying a Spirit Slot.
2.) Slowing Hex is targetted (making it much easier to hit, the mines have an arming delay after you launch them making them a skill shot) which has many advantages to itself.
3.) The mines do NOT silence mobility abilities. Yes, it can slow people down, but it won't stop a Wraith from Teleporting away, or a Calico from using her Leaping Slash or Ult on you. Slowing Hex prevents ALL of those abilities.
4.) Mine Launcher costs 3500 souls, twice as much as Slowing Hex.
The Mine Layer exists as a 500 Item specifically because it's damage is low, but disabling effect of the mines is very handy though most effective early game. Mid-late game most heroes will either have access to items like Warp Stone, or more regular use of their mobility abilities. Therefore, in order for the Dash-locking effect to be worth considering, it needed to be cheap.
The Mine Launcher needed to scale up the damage of the Mine Layer. Doing so to a value that I felt would be useful in a single burst would have made the item too strong, which is why it's damage is pretty low for a 3k Item (Alchemist Fire does something like, 350-400 damage over the duration and has a powerful damage amp rider) but it has multiple charges.
I will probably reduce the Mine duration. 60s is longer than it needs to be. Something like 25s is probably sufficient for farming as well as escaping a chase.
Also, I don't mind some harsh criticism. I would rather someone tell me how things are than sugarcoat it and let me think a situation is better than it is.