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 excerpt taken from the online blog of Ryan, a trans-species zebra after his visit to the Conversion Bureau. And his own views on the stereotypes, misconceptions, following the reality crash between Earth and Equus, and the release of deadly energy that forced the human race to adapt.

I've always loved my six best friends since we were just kids. But now that we're older they're acting differently to me, and I find myself acting in a similar matter to each of them. Our feelings for each other is becoming much different. Will our friendship remain true as we go on with our lives? I wonder.

Cover art courtesy of Duke Moon II

Tropes Page here: The Girls of My Life

With the sirens dealt with and no pressing time limit to return to her world now that she can come and go at will, Twilight spends some time catching up with Sunset Shimmer. She asks a question that has been on her mind for a while now. Namely, how Sunset ever thought invading Equestria with a few hundred zombified high school students was a remotely workable plan. It turns out that radically altering your entire physiology and brain chemistry doesn't do any favors for your IQ.

T for language, alcohol, and slight lewdity.

Probably the best thing to happen in Discord's long life was finding the magic of friendship. As much as the old Chaos Lord might complain, without it he would never have found so many that were dear to his heart.

When that heart finds itself empty, he comes to the Princess to ask a favor: allow him the opportunity to bring friendship to other dark hearts. All she has to do is lend him a statue.

The rest is in his chaotic claws.

Featured on 10/18/19, 10/22/19 and 10/25/19!

Featured in Equestria Daily on 6/18/2020 and in their 40 Fanfics to Read for Villain Day on 11/12/2020!

Reviewed here by Javarod!

Also reviewed by PresentPerfect with the rating of Highly Recommended! And it also made the Top 10 of 2020!

Death tag - no horrible murder, just a few mentions and the natural consequences of time.

Pegasi aren't the only intelligent species which can fly, and the Wonderbolts recognize that. There is no racial restriction placed on the open tryout sessions and over the centuries, the team has had a few unusual members. They have proven methods of working with griffons, self-levitating unicorns -- anything known to get in the air might find their place.

However, it's probably safe to say nopony was expecting a minotaur-sized duck.

(Written in celebration of the revival.)

Now with author Patreon and Ko-Fi pages.

This is a fic based on the Time Loop Files, the format of which was first codified by Innortal on fanfiction.net.
Here's a brief guide.
The basic idea is, one character (the Anchor, usually the main character of a fictional setting) is looping back to the very first moments of their parent series every time either they die or some kind of time limit expires. They of course end up monumentally stir crazy given enough time.
Eventually others start to loop as well.
The reset is not always perfect. Sometimes a loop's history will be different to the "prime" loop, or canonical plot.
"Crossover" or "Fusion" loops also occur, randomly. These can involve the home loopers having a guest, or the anchor for one universe spending time in another, or replacements of one character by another.
Vacation Loops are where the Anchor (or others) decide/s "buck it" and lets off steam by doing whatever comes to mind. There's little or no attempt to maintain the original timeline.

In addition, and particularly more recently, it should be known that this story has a collaborative element to it - people may submit loop ideas or loops, ideally at the Spacebattles thread (a link to the current version of which is on the Trope page), and they may become included.

There's two page image options, thanks to Filraen - the current page image has been edited by the original creator from this work of theirs.. The other one is here:
http://hourglass-vectors.deviantart.com/art/MLP-Loops-466030169