Maybe, but if it was possibly to get both the effects of crystal pendant + the effects of whatever strongest amulet you have, then you would be able to get the more out of it in the long run from your strongest amulet while also being able to get the motherlode rewards (which we don't know what they are yet iirc, they mentioned something like Cwars tickets, champion srolls, etc. but then removed those from the table since people thought that was overpowered.)
The point being that if you do combat you have to choose between better stats or motherlode rewards while skilling doesn't have to make that choice.
Unless they did say what all the rewards would be, then if it's possible to get all of those before the Elf City comes out by doing combat and using your strongest amulets instead of the crystal one, then sure.