I mean it kinda makes sense from a personal experience. I haven't played much in the last two seasons but from my experience. Mercy is still relatively safe without insta rez, you're usually pumping out rez's in 4/5man groups. This is from playing w/ my friend around 2-2.5k rating, he always priority rez's me unless the tank is down and 8/10 its happening even if we lost the point and just delaying. At around 3.5k-3.9k, shes still a relatively hard target to execute, not impossible just rough because she will get hit 50% then fly to the top of the map and in a short time she back to 100%.
Not that this is the reason, but it makes sense in my head. From the sounds of it, she still seems solo queue requirement, less, but still a pretty viable -need- rather than -want-
I feel they might want her in a combo, like if she ults and is w/ lucio's beat drop or inside trans. Or any other character ult. /shrug It feels more like its "mercy ults down, go!" rather than "ults up, go!"