I love D&D, and one of my earliest games a player asked to play as a homebrew Alchemist they found. I initially said yes, but I reviewed the class again and saw that it was just a reskinned Wizard (literally used the class verbatim, except "magic" was replaced with "alchemy/technology). I wanted the player to have more fun with the class so I designed and iterated on this class for several years.
This homebrew was not only one of my first designs in any form of gaming, but it was a great experience in multiple iterations, as I posted several versions of the class on r/UnearthedArcana, which received a lot of feedback which I then took into account for the next version. In the end, the class is a little over designed while being underpowered, but I still look back at the class (and the feedback it received) fondly as my first foray into game design and balance. It also quickly taught me that players will often overlook obvious game balance as long as everything looks very clean/polished, for better or for worse.