I don't really agree with this list for the most part. Here are my opinions.
Knife Juggler. This is an undoubtedly excellent card. However, the thing with it is that you don't really want to play it too early, because then you won't be able to play other minions on the same turn, and thus won't be the most effective. And when it is played later, it becomes really easy to take out. Plus, it's random nature definitely decreases it's value, although it can make it a little more infuriating. I really don't think nerfing it's attack would change anything, though, because that's not the reason that people play the card.
Murloc Warleader. The thing with this card is in order for it to be effective, you need to already have a decent number of murlocs on the board the turn before you play it. Plus, as soon as it's taken out, all of it's buffs disappear. On top of that, murloc decks really aren't run very much at the moment, so nerfing a crucial part of an already underused deck seems completely unnecessary.
Savage Roar. Yes, the Savage Roar and Force of Nature combo is good, but it definitely isn't better than Pyroblast for the simple fact that it requires two cards as opposed to one, meaning you're less likely to get the combo and you have to invest more into it. Additionally, it can also be slowed down by using taunt, unlike Pyroblast which can only be stopped by Counterspell and Ice Block, both of which aren't used very much and are only available to mage. Finally, using Savage Roar in any other circumstance requires that you have a solid board, in which case you're probably already ahead, making this more of a win more type card. It's still good, don't get me wrong, but it's not blatantly overpowered.
Leeroy Jenkins. Leeroy is for sure annoying to play against. However, looking at it this way, without any other cards buffing him or otherwise interacting with him, he's basically a Fireball with a downside that you can only have one of. And doing anything to synergize with him again requires investing multiple cards into it, lowering the effectiveness. He also is very difficult to keep alive for more than one turn, even discounting the whelps. And Leeroy + Hounds was kind of BS, but with the Hounds nerf I think that it will be prohibitively expensive to get any of the good Hounds combos with Leeroy.
Faceless Manipulator. This will basically always be a good card. However, because he is completely reliant on there being other good cards on the field, making him a situational play. I've had games where I've sat on a Faceless Manipulator for an entire game because there was never a good time to play it. Good card, and can definitely swing games, but I wouldn't really say it needs a nerf.
Ragnaros. I think I'll actually agree with this one. Ragnaros is flat out too good. There are basically only two cards that I can think of that can reliably trade well with him (Mind Control and Big Game Hunter, if you're wondering), because even if you Polymorph or Assassinate him, he's already done the eight damage. I feel like what they should do is either reduce his attack so you don't have to lose a bunch of you're minions to kill him, or, preferably, change his attack so it's at the beginning of your turn, thus giving you're opponent more time to react (I think this change should also be implemented to Ysera). That said, it should be noted that I don't actually see him played nearly as much as I used to, which mostly has to do with the fact that the meta has shifted to a much more earlygame focus, meaning most of the time you're not going to be able to play your big powerful 8-drop.
Also, I want to add that Blizzard should be more willing to buff cards instead of just nerfing. I can understand them wanting to make minimal changes to balance because of how rapidly the metagame changes, but I really feel like a few buffs could really help some of the less played classes, and at the very least give some classes more viable options when it comes to making a deck. Ultimately though, none of this will really matter as soon as they add the next set of cards in, because then everything is going to change.