But my proof of work proposal for distribution of XRP is compatible with Bitcoin merged mining so how much is really being wasted? Certainly not all the energy. Maybe some of it (very little).
That makes no difference. The amount of mining is determined by the value of mining. Anything that increases the value of mining would be expected to equally increase the amount of mining. All the additional mining, equal to all the additional value, would be waste. The only reason mining isn't pure waste for coins like Bitcoin is because it is required to secure the currency.
Essentially, you are arguing that it's better to waste and destroy resources than to use them to promote Ripple. You are arguing that it's better to make people do pointless work to "earn" XRP than give them away for free.