You're right that it can't hurt, but the difference is, reading how-to books isn't how you learn the craft. Ultimately, the way you learn to write well is to read a lot and write a lot, and that's it. Sure, read how-to books, but just because it naturally falls into your cycle of sci-fi/fantasy/horror/romance/comics/history/mythology/politics/etc. books. See what I mean? Read everything, write a lot, that's how you learn.
Reading how-to books is certainly how I learned some aspects of the craft, and how I came to understand others. I've discovered new techniques more than once while reading how-to books, and I've learned how to actually use other techniques with more skill.
I believe all information is as useful as a person makes it, and while trying to learn how to write well simply by reading fiction and writing fiction is certainly possible, it's far from the be all and end all of the process, and is certain to leave gaps in knowledge.
One thing I learned early on in college is that proper analysis and true criticism can be very helpful, and so can having writing techniques and methods broken down and spelled out. And having such techniques and methods broken down and spelled out by someone who really knows how to do so is a heck of a lot easier and faster than searching for novels that use such techniques, and writers who use such methods, and then breaking them down and spelling them out for yourself.
There's no need to reinvent the wheel to build a cart, and no need to rediscover
pi in order to learn math. There should also be no need to rediscover all the useful writing techniques and writing methods on your own.
Reading much and writing often are probably the most useful things any writer can do, but they're far from the only way of learning many things about the craft, and are often the long, slow approach.