You know, this brings another thought to mind of cross-classing subclasses. I'll start a new thread: 5E - Cross-classing Subclasses and Multiple subclassesWell, at least those are only at-level-up choices. In play choices, like, what spells to prepare, which spell to cast, etc, can have an even more chilling effect.
But, to address them (1) is optional, don't opt in, problem solved; (2) OK, there's 40 sub-classes just in the PH, and they've been adding them pretty rapidly. But, it's a choice you only make once, at low level, and it's over. Usually, it should be dictated by concept. Some concepts simply aren't covered by a class, yet, let alone a sub-class, and a big part of the problem isn't so much the number of choices as the lack of flexibility or the excessive specificity of many of them. If your concept is perfectly handled by a specific (sub-)class, you're fine, off you go. If not, you're stuck weighing the pros and cons of two or more un-satisfying options, and tinkering around with builds to try to finagle what you're after.