Keras is wonderful. I can't understand whether your comment is in favor or against it. Either way, could you share why?
Keras is great for easy problems. But as soon as you want to color outside the lines its opinionated simple model just gets in the way. Every time I've tried to use keras for real work, it was a total pain in the butt. Do your homework in keras. Use something else for real work.
As the originally-posted-link suggests, Keras is a great way to start in ML (this is how I started, with the book Deep Learning with Python by François Chollet, the creator of Keras). And after one is comfortable with the concepts and the general flow of things, and if one needs to do more advanced stuff (as you say), then move on to something like PyTorch (I love that they mention PyTorch Lightning in the article).
I used fastai quite a bit with PyTorch and ended up feeling the same way. Great for spinning up an effective model in a few lines, but really tough to make it do exactly what you want it to do.