You're talking about different things.
First, it's a guy from Remedy. His point of view is not universal. The Rockstar, Codemasters, etc. guys would say different points of view.
Second, BC is other story. Please, study about gen9aware.
Third, ESRAM was more difficult for Xbox One in 2013. Harder do have good optimization on game engines. In 2015 no one was talking about ESRAM anymore. They found the best optimization on game engines and it's ok. The Remedy guy was telling the same point about GDK. Xbox One was using XDK, other SDK. The new GDK, unifying PC, Xbox One X|S and Xbox Series X|S in same pipeline possibly demmands more code engine rewrite for Xbox next-gen consoles. With game engines completely rewritten in couple years, this subject will be done.
And his opinion about GDK is not universal. Wanna examples?
Read about this Dirt 5 interview, Source:
https://news.xbox.com/en-us/2020/06/10/inside-xbox-series-x-optimized-dirt-5/
Q: What is it like developing on Xbox Series X?
A: Transitioning development to a new console platform, like Xbox Series X, is usually very painful. You have to deal with new tools, new workflows, new ways of thinking.
This time around the team at Xbox brought me a new toolset called the Game Development Kit, which they already had up and running on Xbox One.
This meant that we could make the transition much earlier. In fact, we started doing the groundwork for Xbox Series X development long before we even received the hardware. This kind of thinking from Xbox allowed us to get a real head-start on next-gen development, so after receiving our early Xbox Series X hardware, we were up and running really quickly.
For me, the most important thing in making a videogame is the relationships. Working with Xbox, is a partnership – the team at Xbox is committed to helping us make a great videogame and they’ve shown that to me again and again. That means being open and honest about our experiences; what we’ve loved and perhaps even what we’ve found difficult in development has had meaningful, visible impact on the updates that I get for the tools for Series X. (Shout out to our development partner at Xbox, Richard Hackett! Thanks Rich!)
I’ve never worked on a console launch where, while we’re still months away from release, the tools have been this mature, this stable, this easy to work with.