Mind you, there are two types of under screen fingerprint sensors: optical and ultrasonic.
Optical blasts the finger with light and forms a 2d scan. It's pretty slow and arguably worse than conventional (capacitive) scanner on the back of the phone.
Ultrasonic, however, because it uses sound waves, maps a 3d scan. It is significantly faster than conventional scanner, and it also doesn't care about your fingers being wet.
Ultrasonic sensor only requires a quick tap to unlock the phone. It's actually really convenient to use, I like those. I'd take the capacitive sensor over optical one, though.
I work in IT as PM, you're pretty close.
Modern technology is glued together NOT random shit that somehow works.
Everything created has been built with a purpose, that's why it's not random. However, the longer you go on, the more rigid the architecture becomes, so you start creating workarounds, as doing otherwise takes too much time which you don't have, because you have a dozen of other more important tasks at hand.
When you glue those solutions together, they work because they've been built to work in a specific use case. But it also becomes more convoluted every time, so you really need to dig to fix something you didn't account for.
Then it becomes so rigid and so convoluted that to fix some issues properly, you'd have to rebuild everything, starting from architecture. And if you can't make more workarounds to satisfy the demand? You do start all over again.