Tell me about it. The 2e plague returns!
But we ran into an issue: making everything a subclass is extremely limiting, especially for broad concepts such as a mounted warrior, a holy slayer, or a preacher who belongs to an order that maintains temples and congregations. These archetypes and concepts are deeply ingrained in the Al-Qadim and Zakharan setting, however, and we couldn't just ignore them. It also seemed silly to have multiple subclasses for the same concept (covering different classes). Early ideas to make more generic subclasses that could be taken by ANY class died fast and hard, especially since not all classes get their subclasses at the same level.
In addition, others have published excellent collections of Zakharan subclasses and we didn't want to reinvent the wheel, flood the market, or just copy what they had done.
Our solution was a sort of enhanced background: a roleplaying concepts paired with a minor mechanical boost that a character can generally take at 5th level or so. Most give advantage or proficiency in a skill, in a specific application, and have minimal mechanical impact on the game overall (at least across the course of our playtesting). They're easy to implement, ignore, or just use as a roleplaying aid.
These kits have some of the same problems that kits of old used to: they're by nature not all of equal power level, not everyone uses them (obviously!), and some are very niche and/or specific in their application. But none are likely to break your game, whether or not you use them.