So for XMR, I see 67/67/66/60%, I assume, it means it's more unprofitable to mine XMR, to earn ETH? Is that it?
As you suppose, and as it Is written on the webpage, GPU mining is compared to ETH mining.
XMR reward is lower and it always was is the past so there is no point in mining it.
My next question is, does whattomine website take consideration of existing difficulty level for both ETH and XMR?
Yes, it does.
What would it consider to do its calculations otherwise?
Just go on mining ETH or ETC, there is no point in switching this days