In many circumstances it is. I wrote an essay that describes the thesis statement issue: "Paul Graham and not being as right as he could be in 'The Age of the Essay'" (https://jseliger.wordpress.com/2011/12/02/paul-graham-and-no...).
I've also discovered from teaching college freshmen that having a thesis statement usually improves the quality of their work product. But experienced writers working in some genres don't need thesis statements and indeed would be constrained by them (that's one of pg's points in "The Age of the Essay:" http://www.paulgraham.com/essay.html), and inexperienced writers probably need thesis statements to avoid a document filled with random thoughts. In this respect thesis statements are like training wheels.