The pantsuit isn’t a bad concept to add to the story if it was designed better. Pantsuit was first introduced in the 1920s but this story is probably in the Victorian era. So the 18 century. Horse riding outfits is completely different from pantsuits and it isn’t exactly formal uniforms so it’s natural for you to not mind horse riding outfits since they’re basically pretty basic designs and styles and completely different from pantsuit since it’s a two piece outfit while pantsuits are typically one piece outfits. Pantsuits could definitely be introduced in a historical time period if they just took the time to design it in a better fashion. I’ve seen some manhwa do the historical pantsuits look perfectly without it looking too gaudy and makes you hate the overall design on the character. But it also depends on the art style as well.
That pantsuit is a mockery to all things fashion. Like it's not bad but it looks off. Just draw a damn dress or stay out of historical time periods @ the isekai industry. Horse riding outfits are the only time I've seen a pants centered outfit not come off cringey and pulled off correctly