Both very different songs to "Mercy" there. "Molitva" was an extravagant, over the topic power ballad that set out to impress with it's delivery. That was a showstopper from when Eurovision was all about "BIG" sounding songs. "Amar Pelos Dois" was an achingly beautiful ballad with a sincere delivery. You didn't need a translator to understand it was coming from somewhere very deep. "Mercy" is an electronic song that's minimal in style and unless you speak French, I think it's difficult to decipher what it wants you to know and feel. I had no idea it was actually a song that was highly emotional lyrically until I was told.
A lot of songs are proving to us recently that music transcends language barriers, but i've got doubts about this one.
I 100% agree on what you said. "Mercy" may be cute for now (with only two songs out in total), but I can't see it stand the test of time with 40+ entries in Lisbon, and 26 entries in the final.
The issue for me is that - while the lyrics indeed convey a serious (and not uninteresting) message to the contest - neither the song nor the performance are particularly stirring or in line with a mood that could massively touch people's hearts regardless of their ability to grasp French.
"Molitva", "1944" and "Amar Pelos Dois" aren't appropriate comparisons for me either because all of these entries both allowed heartfelt vocal interpretations (from charismatic performers) and were unique musically speaking in their respective Eurovision editions. "Mercy", on the contrary, remains a commercial electro-pop effort that's more likely to suffer from competition imo, it doesn't leave a lasting impression.