The buyer of the lake is playing by the rules that were set up by the county who is looking out for the taxpayers.
If there is any evidence that proper notice of the tax-delinquency sale wasn't given, or that the county gave special notice to the current owner over and above what they gave to the rest of the public, or both, then I'd agree with you.
However, it seems to me that the value of the homeowners' property has now declined, thus offsetting the value of the gain in value of the lakefront property. Also, what is the basis for reassessment? Just because he's asking $30K per parcel doesn't mean each parcel is worth that amount. None of the homeowners have indicated a willingness to buy.