it's the other way :D, since i bought the house in 2015, my gains are paper gains (~200%), but my property taxes are real loses, since they've grown almost twice as well.
Most municipalities will first establish how much tax revenue they need, then look at the total property values that's taxable, and then set an appropriate rate. If property values double but municipal expenses don't, they can and do lower the property taxes. It's not a 1 on 1 relationship but given average property tax income as a percentage of total income has slightly come down over the past decades, it's clear that tax rates are being reduced as property values go up.