He initially, very early on (like early 2018), was known for having true and false info mixed. I believe there was also some false Smash leak before Ultimate was revealed.
However, since then, he seems to have gotten his sources in order and has said he only leaks things when he has enough sources agreeing on it to where he’s very confident in it.
This is why he didn’t specify Hero, and for the better part of a year only mentioned “Square-Enid character.” He wasn’t certain on what it was, and didn’t want to give out false info that would damage his credibility.
So yeah, as far as I know, everything he’s leaked regarding “Smash Bros Ultimate” has been true. The one thing we don’t know about yet is the “Minecraft content” he’s been saying for over a year, but as far as I know he says it’s still coming, and I wouldn’t be surprised if it’s a Mii costume alongside Banjo.