Reverse engineering as you suggest is possible, but we wouldn't be able to use a number of their keywords just because of their nature. For those keywords we can copy, we use them in the ways recommended by @forexbrokr, @hitmeasap, @taskmaster4450le, and other SEO experts here.
SEO is a long game, and it never ends. Newer content benefits from older content (in terms of authority), and older content benefits from newer content (in therms of freshness). It's like a circle, and circles have neither beginning nor end.
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