The main problem is that there's currently still very little cost to bottlecrowing for a coordinated team. Teams aren't gonna run into issues where mid is foaming at the mouth about his bottle while void's trying to get his midas recipe to him in the safelane like pubs do.
I'd really just like to see bottle slow down the courier to the point that it's both dangerous to frequently bottlecrow (making courier easier to snipe if you know the path it's taking), and that constant bottlecrow (as opposed to occasionally sending the bottle back when the crow's already heading back anyway) almost demands having a second crow.
I don't have an issue with bottlecrow existing, just that it's far too strong right now and really does let most heroes largely ignore "mid mechanics" like harassing, rune control, etc, which leads to very boring mid vs mid games. I guess it's easier for casters, though, since they can largely ignore mid unless a gank is being performed there.
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I actually think Slark is better than PA as an early game right-clicking wrecking ball. He's very hard to control, basically instantly refills health to full while he's crossing the entire map in 5 seconds, and isn't RNG-reliant, so he's not prone to Lysah Syndrome. Free Heart and free haste rune is pretty crazy.
Slark with Repel is pretty scary.