when they nerfed Sylvanas this was their reason
We want players to have an option of what cards they put in their decks, so cards that feel like they must be in all decks (especially Neutral ones) are not ideal.
So many cards to nerf with that logic!
Loatheb
Azure Drake
Piloted Shredder
ET
and of course Dr. Boom. Pretty sure everyone on ladder plays Dr. Boom now, it's a race to who plays him first. In case you don't see him in a game the player was likely unlucky rather than not having the card at all.
Their reasoning for nerfing cards keeps changing every time they do it.
By all standards and accounts, Dr Balanced fits perfectly within their "balance" philosophy for the game in terms of justifying a nerf for it.
And Dr Balanced gets used way more than the 4 cards you listed. It is WITHOUT A DOUBT the most used card currently in top level decks. It sort of gets muddled when you compare it with Shredder because people have two of that in their decks but not every deck uses Shredder (like Handlock doesn't use Shredder, neither does Patron/Control Warrior for the most part).
If you look at the top decks with all the classes that gets used in high level play and see if Dr Balanced gets used in it:
Hybrid/Midrange Hunter: Gets use
Tempo Mage: Gets use
Handlock: Gets use
Grim Patron: Sometimes get used depending on the list
Control Warrior: Gets use
Midrange Zoolock: Gets use
All Druid decks: Gets use
Oil Rogue: Sometimes get used depending on the list
Midrange/Control Paladin: Gets use
Control Priest: Gets use
Midrange Shaman: Gets use
Mech Shaman: Gets use
Mech Mage: Gets use
So basically gets used in the top decks for all the classes and sometimes gets used in two other top decks.