That's not evidence. You want evidence? Look at the trailer.
-Worked on with HAL Lab + dubbed as "original title"
-BOTW Link (this one is debatable, but it at least confirms it isn't a STRAIGHT port)
-New characters - the inklings, also confirms it isn't a straight port
-If this game was a port, we would've seen gameplay
-Sakurai said he was working on the game silently day by day. I don't think a port would require that much effort
The only thing that suggests it isn't a new game is the fact that they're planning to release a NEW smash in 2018. Unless they're going the melee route and are going to complete this game in a very short time, there's just no way they'd have enough time to make a polished Smash game that isn't somewhat reminiscent of Smash 4. We can definitely expect a lot of reused assets in this new title.
The whole point of this thread is to point out that this game has had enough time to be a completely new game. Brawl and Wiiu/3ds only had between 2 and 2.5 years of development. With the lack of a 3ds game this time, the devolpment should be shorter than last time.
If development started in 2016 and this game releases for the holidays this year then they should have had at least 2 years to make this game. That is in line with the development time for brawl and wiiu/3ds.