I would shift it to pure wonders. Wonders are an absolutely known quantity, you know the absolutely maximum impact they could have on the archeology race (and prevents things like generating more ancient sites than are allowed type of thing).The more I think about it, the more I think either the city part or the ruins part is superfluous. You can (and lots of people do, as I understand it) play without ruins, so it has to be that one really.
I will update the OP to scratch the ancient ruins part. I think it's unnecessary variance (sometimes you get like 7 ruins!)
You might need to make the obelisk cooler to compensate but no issue with that since it requires a wonder.