> trade secrets do no good at protecting the invention.
This, IMHO, is the wrong issue. Invention shouldn't need protecting. What needs protecting is your ability, as an inventor, to move first and reap benefits from that alone. Trade secrets work pretty well for that.
If, then, your invention is so non-obvious to others, it will take them much longer to reverse engineer it. Which will give you even bigger advantage. If it is more obvious, you will lose this first mover advantage rather quickly, as you should, because the invention was fairly obvious.
On the other hand, patent systems gives the same number of years to all inventions, making the obvious one real obstacles to progress.