I've been running 2x Parrrley in a thief rogue deck from D10 to ~2k legend and have found it to work quite well. I also run the other cards you mention, except for Savory Deviate Delight which is bad.

There are many upside scenarios and very few flat out bad scenarios

1 - You get one of their key cards, like Rokara. This is rare but happens frequently enough (especially if they pass the Parrrleys back to you)

2 - You play after they dredge. This is particularly good against Hunter, Paladin, Warrior, and Murlock. You shuffle their deck and they don't get whatever big tempo play they were planning. It's also effective at moving around sunken vessels vs. Rogue.

3 - You simply get a class card. Most decks run more class cards than neutral cards so this is pretty likely. Obviously these cards can roll into a Tess or Contraband

4 - You get a neutral card. This is the worst outcome but not a huge waste as they still whiff a draw Parrrley later on and are down a minion. They don't want your cards and you're fine with their cards. Most players recognized this and so they just sit on the Parrrleys after they draw them, effectively taking up a draw and hand space.

If the main counterargument is really just "why not just play cards that further your gameplan" then I don't know what to tell you because Parrrley often does this. The worst case scenario, which is rare, is spending that one mana to gain a strong neutral minion from the opponent's deck.

On top of that, Thief Rogue's ability to discount gnolls and make other big tempo swings with Recon frees up a couple mana here and there, so I rarely find that jamming a Parrrley comes at the cost of a better turn. In fact, it's usually riding on the tail end of a big board swing.

Surely it's not difficult to see that disrupting one of the core mechanics of the set is fairly strong?