First up, druid's embiggen doesnt have a sufficient downside.. compare it to priest surrender to madness where for the same benefit it costs 3 mana, and destroys 3 mana crystals, severely hampering your tempo before you see gains, although minion costs remain the same. Where embiggen costs 0, and increases the mana by 1 to a max of 10.
I see a solution to be one or a combination of increasing the mana cost of the spell, removing the cost limit forcing you to think when using it in case you create unplayable minions (although these minions can still be summoned by other means), changing the rarity to legendary so you can only have one copy, or increasing cost of cards affected by 2 or 3 mana.
The second issue i have is with Murozond, the text states to play each card the enemy played the previous turn... this would infer that minions with battlecries would trigger (because it says play not summon), but they do not. Also minions with stat bonuses also should retain those bonuses. If the text was "play each spell and summon each minion the enemy played" then that is how it's acting currently, but it doesn't read like that. Murozond should be changed to include the battlecries of minions, and retain the stats of said minions.
I literally couldn't agree more about murozond. They would argue they couldn't say "summon" because that wouldn't apply to spells, but it is still worded like trash. When you PLAY a card, it gets its battlecries. When you summon it, it does not as you stated.
It would also make the dragon more interesting and difficult to play around, which it should be at it's cost. It also happens to be a card that doesn't really fit into any priest deck they are trying to push either, so it being more powerful (working how it should) would be fine.
People always complain that there's never anything but Rez priest and it's so dumb to play against, but you can only use what is given to you. And blizz doesn't give priest crap, and everyone knows it and agree. Hell im sure priest players wish more than anyone there were more options.
Sorry this is not a Rez priest post, kinda just drifted there. But I agree with both your points.