Trust me, I would not be impressed with this either. The development time for Kraut Buster has been much longer than other games. In hindsight, maybe it should have been funded with reprints of other titles. After 180 days, you can't refund via Paypal, so someone is going to have to eat it. They should have sent it via gift but even if they did Mike would still be out a chunk of change.
On the flip side of your argument...if the Euro had increased in value, should NGDev adjust the refund down instead? There is always a currency risk involved in payments like this. The Pound took a shit after Brexit so I guess any Brit that wanted a refund would now make a profit
There could have been a no refunds policy. While far from ideal, at least most of the money was returned.