I'd agree, sequentially worked far better for me although I understand Kaplan suggests skipping around. Even logically, I can't understand how one could read the first paragraph for a minute or two, then decide the passage is too tough, then try to get that subject matter out of one's head in order to try the next passage, which also might be considered too tough, etc.
Even psychologically, if one attacks passages with the intent of conquering them and fully understanding all info versus "testing the waters" to see if that passage is too tough to tackle initially, I can't see how it makes sense to go in anticipating acknowledging that some passages are too tough to handle. Wouldn't that make them seem even tougher when coming back to them later? This test is geared to psych test-takers out, why allow the exam makers to succeed?