Just like you can be 99.99999999% certain that your properties will eventually be satisfied when the fancy compiler turns it into equivalent code.
If your program is truly nothing more than that "if" statement then there is unlikely to be any productivity gain, just as there is no real productivity gain using a programming language over flipping toggle switches for something so simple. Programming languages would have never been invented if that bit of logic summed up the entirety of computer science. In the real world, the calculus starts to change when you are trying to solve bigger problems. A lot of solutions require way more code to implement than to describe the necessary properties of. That is where you can gain some huge productivity gains by being able to focus on declaring the properties over having to define the full implementation.
But, again, it is not a panacea. No such thing exists. Every abstraction brings its own set of tradeoffs. Your job is to find the tradeoffs you can accept for your unique circumstances. What others are doing is irrelevant to your situation, but it remains that others are doing things and it can be fun to learn about it.
If your program is truly nothing more than that "if" statement then there is unlikely to be any productivity gain, just as there is no real productivity gain using a programming language over flipping toggle switches for something so simple. Programming languages would have never been invented if that bit of logic summed up the entirety of computer science. In the real world, the calculus starts to change when you are trying to solve bigger problems. A lot of solutions require way more code to implement than to describe the necessary properties of. That is where you can gain some huge productivity gains by being able to focus on declaring the properties over having to define the full implementation.
But, again, it is not a panacea. No such thing exists. Every abstraction brings its own set of tradeoffs. Your job is to find the tradeoffs you can accept for your unique circumstances. What others are doing is irrelevant to your situation, but it remains that others are doing things and it can be fun to learn about it.