I mena it works in Dota 2 and it is actaully a highly competive item agaisnt some heros there.
In DotA 2 there are item actives that:
- Allow you to knockback your allies into your enemies
- Grant 5~10 seconds of invulnerability and untergetability to magic damage and, for most intents and purposes, immunity to all CC for that duration.
- 15 seconds of invisibility
- forced suicide to deny an opponent gold bounty and most XP bounty
- Stasis on anyone you want
- Flash on a really-low (albeit out-of-combat) CD
- 200% life steal
DotA balance is apples to oranges with LoL in most regards.
Several things that work in DotA just wouldn't work in LoL and be increadibly OP.
A solid range of things in LoL that are balanced would also be OP in DotA.
It's also worth noting there are no AD or AP ratios in DotA: so the things items need to do there and how champions scale is quite different.
Concerning the issues with an active on Thornmail in LoL:
That would hard-counter a wide selection of fighters by forcing them into an unwinnable position.
While also doing pretty much nothing to marksman, several of which can easily bide their time using abilities and re-positioning until the effect wears out.
It's worth pointing out that it's entirely possible to build a team-comp without any fighters, but each team is always going to run at least 1 marksman: so not a healthy direction to direct the game.