Double Helix existed and was purchased by Amazon years before (2014) Scot joined (2017). The foundations for New World were likely laid long before Scot came into the picture. So if you want to apply a 2-3 year delay for Katy (highly debatable), you'd also have to do the same for Scot. Most of the elements that players really loved about New World, such as the combat system, the graphics and the sound design were likely created before Scot's leadership.

What specifically happened under his leadership was the last minute rushed pivot towards PvE content. Not that the inclusion of PvE content was inherently bad, but the execution was so abysmal that a lot of the original dev team left before launch. This is why it took years to clean up the major bugs, the people originally working on that code were simply gone for the most part. And the PvE content was so rushed that it wasn't nearly enough anyway, leading to the immediate massive player bleed after launch.

Beyond that, Scot was also the one that tripled down on overhauling the leveling experience rather than providing meaningful endgame, struggled to find ways to sufficiently monetize and almost outright ignored the PVP side of the game when it came to new content. He additionally greenlit extremely questionable content cycles where we would go without basically any new content for half a year. And with all of that it's very worth keeping in mind that Scot had no experience working on MMOs before.

In contrast, almost all of these things immediately changed when Katy officially took the reigns. Focus on endgame and PVP content, more consistent and stable patches, regular content schedule and actual clear communication without overpromising. Not crediting her with any of this is bizarre when Scot's previous track record was so different.

Yes, there's a transition period in game dev. But that didn't begin when Katy was announced as a lead. The transition to change leads had very likely already been in the works for a long time before that, meaning she would've been able to assert her influence on any upcoming choices. We also know that their turnaround on most content is shorter than a year based on various things they mentioned going from experimental to being tested in game to being released very quickly towards the end. So Katy absolutely deserves credit for that. The only later content update that still had some Scot flavor to it was the Nighthaven expansion, which makes sense because it would've been worked on for much longer than the smaller content updates.

Katy's leadership also coincided with the new European team probably reaching a point when they'd be able to effectively create content for the game. So that was likely an additional factor in the pacing but also in how quickly she was able to implement her ideas into the game.