That's just sad, you forget that it's actually a partnership and not one manufacturer borrowing engines from the other
Big difference between a partnership sharing technology and borrowing engines from each other.
Both is possible, it can be a Merc engine with ideas and tech borrowed from Nissan / Renault, or it can just be a straight Nissan or Renault engine with a Merc badge.
Can be taken a step further, a Nissan engine with tech borrowed from Renault or the other way around.
If it's a Merc designed engine with borrowed tech it's fine, if it's a Nissan engine with borrowed tech it's fine, but if it's a Renault engine then no thanks.