Yes launch aligned Switch have sold more than PS4, but not in any way similar to the difference of switch launch window+holidays versus PS4 launch + first march and april. And again if there was more inventory PS4 and Switch would have sold more on launch, showing that for launch it being on holiday doesn't necessarily improve sales that much.
It is beneficial to launch as early as possible, if holiday would be so much better then why didn't Nintendo wait for Holiday in 2017 to launch? Sony had released outside of holiday in the past. And you can bet that if Nintendo could have launched on Holiday 2016 they would have, but that is because they would like to launch earlier than later.
If inventory is there both can possibly outsell it.
Because the Wii U was discontinued in January 2017. Nintendo wasn't going to go 10 months without a home console in the retail space. Nintendo was getting such bad press at the time, "Nintendo should go 3rd Party", that they had to launch a new console ASAP. And that's what they did.