I am well aware. Jade Druid was generally at the bottom of Tier 3 and often Tier 4 during MSoG; it was definitely nowhere near a broken deck at the time, especially since Reno Warlock was one of two meta tyrants despite the erroneous claims that the deck “killed control.”
But the problem was Jade Druid was twofold: [1] it was a ticking time bomb that would eventually have become utterly degenerate if not broken, and [2] the mechanic was inherently extremely polarizing.
For the former, we saw what happened due to 5-Mana Spreading Plague and Ultimate Infestation in Knights of the Frozen Throne.
For the latter, this was true even when it changed. Jade Druid’s match-ups only flipped after the KotFT balance patch: with Spreading Plague and other defensive tools, it started to become good against aggro; but because of Skulking Geist, it started to become bad against control.
Raza the Chained was entirely similar: a ticking time bomb. People did not seem to understand how far above the power curve he was – he is still quite a good Legendary in Reno Priest – because Reno Priest originally often floated Mana anyway. More saliently, people do not seem to recognize that his previous mechanic was inherently broken; 0-Cost cards and abilities are extremely dangerous. Raza would have been the reason something became broken later down the road, even if Shadowreaper Anduin had not come along in his current form. This was one of the few nerfs in which exactly the card that should have been targeted was.
I am blaming Mean Streets of Gadgetzan because it developed and pushed these inherently questionable cards and mechanics: its bad design and balance is what initiated and exacerbated all the problems in the Year of the Mammoth. All expansions have cards that could potentially become broken, but usually they are due to more problematic cards (e.g., Juicy Psychmelon vs. Aviana); in this case, the cards that completed the puzzle were only almost as problematic at worst.
Reno Jackson was necessary because he was Warlock’s only reliable way to heal at the time, so that control was pigeonholed into Reno decks both out of necessity and relative power, as well as Mage’s best way to heal, especially with how well it worked with Ice Block.
Kazakus alone was sufficient for Priest, which did not truly require a full heal in most cases, after rotation. This was initially the weakest Reno deck anyway because, while it had by far the best Reno class Legendary, it did not have much to gain from losing consistency, particularly with the overpowered cards the class gained from the same expansion.
That is besides the point, in any case. Reno Jackson made Reno decks a thing; Kazakus was so powerful that he made them better than traditional control decks in spite of the inconsistency. There is a reason the Reno classes are only the Kabal these days; prior to MSoG, they might have been the most natural choices, but they weren’t far better at it than the other classes.