set the sag and it's all good now. the nervous steering is gone, with only 10mm more sag.
about the imbalance, there's about 300 grams of imbalance
i managed to temporarily fix some 200 grams counterweights to the spokes and that too is ok now.
it is very weird to have such a big weight difference though.
i'm guessing a big heavy rim lock along with the cheapest tires...
i'll just wear them out and then replace them with some quality ones.