Key word is "obvious". If you say, "how should you solve games?", the historical answer is "using game theory", and when you say, "what does game theory imply for Newcomb's dilemma?", the historical answer is "two-box". It takes an additional insight to work out that a better metastrategy is possible, and things which take an additional insight are no longer obvious, true or no.

Edit: Alternatively: When I said "metastrategy", I meant one level higher than "two-boxing" - in other words, the level of decision theory. (I'm not sure which of the two objections you were raising.)