The Conversion Bureau never made any sense anyway, but here are some places where it would have made less sense.
Not necessarily worlds where the ponies would lose the fight - just worlds where conversion wouldn't logically work.

Before suggesting a World, read the index to make sure I haven't done it already.

An archeologist finds himself pulled into a parallel world by Discord's storm of Chaos, and encounters the mysterious creatures that live there. How will a rational human, confronted by creatures out of mythology, and unable to find his way home, adapt to his environment? Only one way to find out.

With the Barrier slowly consuming the Earth, and nowhere else to go, the population of the world has little choice other then to go pony, or die.

All but one who finds himself unable to go pony. Instead the potion renders him immune to the Barrier and magics toxic qualities, as well as giving him the ability to use magic that isn't toxic to regular humans. Exposure to more potion won't force a transformation either, only increase his magical prowess...

He stands alone. The only human who will survive the Collision of the two worlds...

...Then again, screw destiny.

Equestria is dying. A one in a lifetime quirk of astrological dimensional convergence has caused a unique fusion between Equestria and a world called Earth. With it will come the birth of a massive superplanet. But ponies will not survive the process. A proposal for the salvation of ponies has been put into effect. But can Equestrian society deal with the losses that come with salvation?

Only the Conversion Bureau holds the ultimate answer to that question.

After 12 long years of conversion movements, Princess Celestia has finally fallen to a small group of human resistance. Now the humans have the means to increase their numbers and have the chance to reclaim their lands. But they will soon learn how extensive Celestia's dark dealings are.

Sequel to The Conversion Bureau: New Tactics and New Tactics Part II Don't forget to thumbs it up if you liked it and want more.

*Anti-TCB story with Xenoponies*

This is a story of the messed world of the Conversion Bureau Universe and one man's dream of leaving Earth to seek a better life on mars.

In a moment of weakness, Chrysalis had more than a taste of Shining Armour's love. 11 months later, Twilight Sparkle finds herself a brand new niece by way of 'A small foal in a basket on my door step'.

Special thanks for the picture by Awilldrawforfood1
Now edited with DoomManta.

Walking with the paws of an ancient predator, a young man finds himself in a strange world. A world where horses are the dominant species, and he’s a very rare and dangerous animal. How will a speechless man turned wolf deal with society? How will he approach ponies? Would he even want to bother speaking to them?

(Love interest is not revealed in any of the current chapters. So don't freak out when you don't see it. I'm also focusing on a very realistic sense of love. This will be a later part of the story when romance becomes truly relevant. Point out ALL errors to me when you see them, even the ones that have been pointed out already, and I'll see what I can do.)

(Special thanks to my EPIC Proof-reader and Editor ultra1437)

It all started with a simple question: What if? What if Luna had ponies who noticed the beautiful nights she created. Would she have turned into Nightmare Moon? Would she and Celestia rule together for a thousand years? Would Twilight meet the rest of the bearers of the elements and become friends with them? Now, with the help of a new magic spell that she created, Twilight is going to find out!

Welcome to the Lunar Republic!

Featured 4/9/15

This story is a sequel to Princess Celestia The Changeling Queen: Stories Behind the Mask

At the Royal Wedding, Chrysalis and the Changelings were revealed to all of Equestria.

But another mask was torn away that day. A mask born for a thousand years. A mask created on one promise. A mask, that has become synonymous, fused, to its bearer.

A mask that when ripped off, causes Twilight, her friends and Luna to question everything they ever knew about the one pony, one very important pony.

At the Royal Wedding, the meaning of the phrase 'Princess Celestia' changes forever.

NOTE: Chrysalis is NOT Celestia!!! That'd be impossible to pull off.

Credits to: Plainoasis for the design of the cover art
Note 2: Original cover art here: https://angelea-phoenix.deviantart.com/art/Contest-entry-Changeling-Celestia-337023552

Pre-read/edited by Zervziel,
Blankscape,
FinalFan,
Courage Fire
Aurora Borealis

Side Stories to this can be found: here.

An audio-reading on youtube up to Chapter 21 is up by StraightToThePoint Studios. I'm aware there are others but this is the nearest complete one: [embed]https://youtu.be/X3eMW673CSY[/embed]

There are also 2 print versions of Princess Celestia:The Changeling Queen. Nonexistent Publications run and Ministry of Image's run.

Contribute to the TV Tropes Page (thanks to Babs_Seed72 for getting it up)