In such a case, FSW would win without any contest.
The visuals are splitted into three categories: the plane, the scenery, and the sky.
Let's start with the scenery:
FSX and P3D share the same default scenery and are quite ugly by default.
FSW has the same default scenery, excepted it's enriched with FTX Global ground textures and autogen textures. Additionally, FSW draws the ambiant occlusion, which gives a more consistent rendering to the objects on the ground (especially with autogen).
P3D can only compensate a bit with its more elaborated shadows.
FSW wins on the scenery rendering.
Now to the planes:
The default FSX planes are now too old graphically.
P3D default planes are also "not so young", although some of them are ex-paywares, which grants them superior graphics and features compared to FSX.
FSW planes are built up from scratch, completely new models.
So FSW would win on the "default plane" graphic level.
Finally, the sky:
Well, concerning the sky, everything is strictly identical between FSX, P3D and FSW. Same textures, just a bit of differences in the shaders leading to strange results in FSW at the moment.
So by pure default, this time P3D wins the match, but that might be just a temporary win, until FSW gets fixed in one of the next updates.
So FSW appears as the winner of this comparison, yes... However, we all know which sim is the best really. Our winner is in reality the worst of the three sims at the moment.
Situation may change with future updates though, and FSW might have a chance to reach... the 2nd position in the best case
P3Dv4 FTW !