Hearthpwn

Legendary cards are the highest rarity and should feel like something with a high impact and the opponent should feel like "How do I deal with this?"

No, thank you. Legendaries should not be stronger than commons. They should enable archetypes, to be unique and exciting but making them the only cards that matter (and this is what you advocate for) is wrong and boring. Hearthstone should stop making stuff like a two-drop legendary that is better than any other two drop no matter what deck you play, not produce more of that.

For example in comparison: why print Thori'belore the way it is? It just does not feel strong enough and Warrior really could need some help

My theory is that it was nerfed based on how it plays with future expansions. Remember that they playtest way ahead of what we see. And I can totally see it being good with a better and larger fire spell package.

If Big Priest ever dominates the meta again, then people need to tech in Silence and Transform effects

I dare you to try that in wild against the current version of Big Priest. To be honest I don't remember silence or transformation working against any version of big priest unless you go for a ridiculous amount of those. Aggroing them down, killing them with OTK combos or having so many removals that you don't care are (and were) the only ways to deal with the big priests