So if thousands of engineers independently worked for years trying to solve some important problem, and then finally a mere two of them come up with solutions around the same time that are similar, you'd say the solution is obvious?

That's a pretty weird way to define obvious. It is true that sometimes a term used in the law deviates a bit from the meaning of that term in ordinary English, but rarely as far as your definition of obvious does. In English, obvious means that it is easy to discover. It should be readily found by any reasonably competent person who looks.

Of course, then you get into a argument about proving independent invention. Given that applications for patents are published, it's hard convincingly show you weren't aware of another person's invention.

FWIW, I agree with the principle. There's a lot of obvious stuff that gets patented, particularly in software.