While i am familiar with the concept that google ranks subdirectories and their child directories with some of the weighting based on their position in the directory structure, I am quite uncertain that this is an actual factor.
At one pont, this was a factor but that was before the implementation of Caffeine, Google's current Search Index. In the olden days, before Iggy Azalea and driverless cars, Google did not "fully" score and weight pages upon their discovery, thus they would make first-order assumptions about pages -- and one of them was that if your home page (the default page at document root) had a "page rank" of 5, then domain.com/1leveldown/subpage.htm would have a page rank of 4 and domain.com/1leveldown/2levelsdown/subpage.htm would have a PR of 3.
These observations were verified by myself and others over and over again, but that was a long time ago now. And there's no real need for that anymore with the current methods of indexing and scoring pages.
URL naming is vastly overrated now, because it used to be tremendously effective on sites of sufficient scale.
If you look at the examples used in the top response, you'll see that the SERPs do not really behave in any relation to the URL structure. What you will often find instead is that the SERPS model the volume and authority of the internal linking to a page.
One thing I can tell you is that " trailer" these days brings up a big Knowledge graph entry that is simply an embedded youtube of the trailer as the first result. "trailer " brings up a host of youtube links first.
My answers to your questions
Is it true that resource deeper in URL hierarchy is tend to be less important when comparing to URLs of other site?
"Yes, all other things being equal, which they never are, so actually, no."
Is sacrificing eaningful, seamless hierarchy worth for this SEO optimization?
"Absolutely not, give google a seamless hierarchy to crawl where everything has metadata and on-page text that reflects the user need you are trying to satisfy with the page, and you will profit.