Hearthpwn

Hrmmmm... no.

The problem is you've presented two contradictory desires. There was a GDC talk about this called 'Cursed Problems in Game Design' where one or more promises made to players are not being met because your other promises to players contradict that promise.

So, here's the problem:

Quote from Magpai_ >>

At this point in time my main gripe with wild is in the inability to play decks I used to enjoy playing.

[...]

As a Wild player, I don't mind losing to better decks, but I do mind not being able to play my favourite decks of the past!

 Does not align with this:

Quote from Magpai_ >>

I realise that everyone will have their favourite classes and cards: be it 1-mana Execute, 2-mana Equality, 2-mana Flametongue Totem, 0-mana Hunter's Mark, 1-mana Mana Wyrm, original Shadowboxer, original Dreadsteed, original Preparation or 2-mana Wild Growth. Notable Neutral cards would be: 5-mana Giggling Inventor, 4-mana Barnes, and 5-mana Naga Sea Witch.

 Because many of those cards were never in standard decks, or continued to be used post nerf, meaning different decks used the card for different purposes.

For example, reverting Execute to 1 mana allows Classic decks to be rebuilt in Wild, but now Even Warrior decks (yes, they were a thing, even reaching rank 39 legend) can't use the card.

Or using the Dreadsteed example - Dreadsteed + Defile was never a combo in Standard or Wild specifically because it was nerfed before Defile even entered the game.

Unnerfing any of these examples will not fix Wild because it would only break your own expectations in other ways - and not because of overall power, but because your expectation doesn't fit with the current rules of the format.

If you want to unnerf any of the quoted cards, you'd also need to implement a system where including the unnerfed versions of said cards also bans any cards that were released after said nerfing, or any card released after those cards rotated into Wild (in cases like Barnes where the nerf happened post-rotation), and frankly, Wild is not a game mode with a big enough player based to implement those kinds of systems.

Classic already exists for this exact fantasy.