I don't necessarily disagree, but to my mind, Ten Hag has reached his ceiling in the Netherlands. His squad will never get much better, he's unlikely to get closer to European success than he did two years ago, and he's been Dutch champion. He's basically 'done' at Ajax, and just risks lowering his stock in case he has a lesser year (which would otherwise be normal every now and then).
Gladbach may not be a natural next step, but I don't easily see him for a top job in England (not sure they'd consider him ready), and if Rose joins Dortmund, then the two German top jobs are also out of immediate reach given Flick's success with Bayern. Gladbach, and also Leipzig, seem reasonable choices for me then, to get out of the Dutch cocoon and confirm his qualities. I'd also think he can apply his tactical approach there relatively well. Come to think of it, Leipzig might actually be a better option if Nagelsmann leaves after this season.
But yeah, maybe I'm overestimating Gladbach or underestimating Ajax; but to me, Ajax is really just a blast from the past internationally these days. (Despite that CL semifinal.)