I didn't say it started under a later ruler. Where is your evidence that it started under a later ruler?
If they would have done the minimal amounts of sacrifices to satisfy the Roman authorities, they wouldn't have had a problem. Much of the time, this was just at the emperor's altar, toss some salt in, and you're good. There was pressure to do that, the Christians refused.
Roman aggression against the church ebbed and flowed, if the same pressure that happened under Domitian happened in the first century, we might not have the letters. If we take a broader look at dictatorial regimes that persecuted Christianity though, the Soviets did their share of infiltrating churches before closing them down.
Will you admit that it is less reasonable to make a counter-claim without ANY evidence of any sort than to go by the pattern of history?