The paranoia here is amazing. You probably regret taking the blue pill and haven't got your COVID-19 vaccine yet because you don't want to be microchipped by Bill Gates.
That's not how you calculate probability, the more minions in play the less chances Felmaw hits face. And no, Naralex is not rigged, from 5 dreams available, you get 2 and they can repeat, that's all.
Do you really understand how probability works?
You CAN rig probability.
Let's say there are 3 types of items, A, B, and C. If there is only one of each type, the chances of getting an A is only 1/3.
However, you CAN reduce the chances by adding more B or C items. For example, there is only 1 A, but there are 3 Bs and 3 Cs. The chances of getting A is now only 1/7.
These two RNGs are the same. You CAN rig them in the code. It's actually pretty easy.
In fact, Hearthstone has actually confirmed that they rigged some of the Discover card's RNG, so that they can't Discover itself.
You're not "rigging" the probability. Probability is just the mathematical chance of a resulting outcome based on the possible choices and desired outcome. Rigging implies it's being faked to appear real while it isn't. Changing the probability based on the number of possibilities is still a probability. What you're referring to is changing the individual outcome of each individual card's fixed probability by changing the seed.
Think of it like lottery scratch off tickets. They know exactly how much money the entire batch of tickets makes before it's scratched off. They will sell the all of the tickets for X amount and all of the tickets unscratched will pay out Y amount. That's not rigging probability. It fixes the probability of each winning amount based on what was printed by the original batch, that's the seed.
In the case of a lottery, every time a ticket is drawn, those probabilities technically change because either a winner or loser was removed from the seed. In the case of Hearthstone outcomes the seed doesn't change after a card is drawn. So whether it's 1 in 5 because there's only 1 of each card seeded or the seed is card 1 has 2 while cards 2-5 only have 1 each, that makes card 1's probability 1 out of 3 while the other cards are 1 out of 6.
It's also possible that they have different seeds for each choice of a discover where you may have a better chance for holy cards in the first choice, better chance for shadow cards in the second choice and an equal chance for both in the third choice. It's completely based on the seed. You can alter the seed so it doesn't self replicate or include more search cards, etc.
Nerfs don't have to crush cards. Sometimes it's subtle changes that actually are the most impactful.
+1 mana to RSW and Hysteria is important. Both are very big momentum swings and delaying them could lessen them to some extent. RSW specifically also makes the absence of an early Incanter's Flow felt a bit more heavily. It's about slowing down the momentum gain for these decks, Priest in to just having a hand full of dominant answers by being ultra efficient with every spell it plays or Mage cruising through it's deck to yearning for the burning.
The change on Crabrider is actually better than a 1/3 nerf. It makes it a slightly more useful play out of rush themes and less of a late game beat stick. Taking it out of late game Paladin's hands with an 8/8 buff that has to wait a turn to hit face twice is not something that should be overlooked.
Mankrik nerf is largely low impact.
First Day of School change(kind of both a nerf and buff) still gives Paladins the board presence it desires but makes it less deadly on first play of the game. It won't change how much it sees play, it will only change how fast salty people concede.
The buffs were by and large non-factors to the metagame. They may have a minor impact on duels? Shaman fans wanted to make an impact and they may still fail to make a dent in the metagame.