The rationalist strategy is not to defect from the beginning, but to cooperate till somewhere into the 90s

That certainly isn't implied by the problem and the agent. It depends entirely on what the opponent is expected to do. I would use that strategy when playing against an average lesswrong user. I wouldn't use it when playing against some overconfident kid who has done some first year economics classes. I wouldn't use it when playing against a CDT bot or a TDT agent.