I'd say the overwhelming majority of writers seem to have this routine writing in the morning.

Certainly, mornings are generally very productive, you get a certain amount of productive time in the morning which is very valuable in my experience. The issue is, for me at least after about 2-3 hours of good real creative work I'm done, there's nothing left in the tank.

No amount of routine or pomodoro or any other system has overcome this, my brain simply feels wrung dry of any more creative ability.

You just kind of flew right past the point of his saying. The point wasn't "mornings are the creative period", it was that you force yourself to be creative by doing it every day.

It's like that other adage about artists and critics. I'm paraphrasing here: "Critics will get together and talk about meaning and form and style. Artists will get together and talk about where to get cheap turpentine."

It's almost you don't worry about the actual creative part of things. Just do things. Most of it will be bad. If you're counting on only creating good things or let creating bad things discourage you, you'll never actually create.

Maybe you do feel wrung out after a few hours, but maybe if you honestly kept at it for another hour, you'll get a second burst. Maybe not. Maybe it happens sometimes, maybe not others. The real point is that unless you try it every day, you'll never find out.