I think this Switch lead will be short lived, maybe even just this one week, as they don't have a significant system seller for the next 4 months until Let's Go in November.
Theres been shortages of PS4 stock though in the US... atleast of the PS4pro.
If you follow the NPD prediction tool thread, you ll see in July the Switch leads, and PS4 & XB1 are more or less neck and neck.
I think the Switch wins July NPD.
Necro-bump this 2020: http://gamrconnect.vgchartz.com/thread.php?id=229249
Bumb in 2021: http://gamrconnect.vgchartz.com/post.php?id=9047071