And there is good evidence that individual Christians suffered far worse under the pagan state religion of Rome than individual pagans did under the Christian state religion.

Are you referring t just in the narrow timeframe of "Rome" as generally defined, or in general? Because of the former this is completely wrong, Charlemagne probably killed more Saxon pagans at the massacre at Verden than the Roman state killed Christians in the entirety of its history. If the latter, arguably the persecutory power of the Roman state greatly increased with Christianization, it was just primarily aimed at other Christians. This doesn't mean pagans did not suffer--Constantine boasted of the large numbers of pagan temples he destroyed, and later emperors criminalized important pagan practices such as soothsaying.

I would also not go so far as to say there wasn't individual persecution. There were laws on the books criminalizing public worship.

Also, the fact that quite a lot of Classical art and architecture has survived to this very day is testament to the fact that there wasn't any kind of systematic attempt to wipe out all pagan culture everywhere.

There are many, many examples of wide scale defacement of pagan monuments by Christians. I once did a little personal study around Naples--out in the countryside it is more common to see defaced statues than intact ones. I think you would be hard pressed to find examples of such sustained, general iconoclasm outside of an Abrahamic context.

The advancement of humanism in the Renaissance is down to Christianity in the first place!

This is a pretty bold claim, that many of the humanists themselves would disagree with.