Eh. I think that's a bit of oversimplification. I work in computer graphics. All of the "old school" companies (been around for 30+ years; Pixar, Blue Sky, DreamWorks) wrote their own renderer/compositor and other tools because they had to. Today most of those companies have shed (or spun off) most all of their proprietary core software. A very few companies (Sony and Disney) have developed newer generations of rendering software--but both of those have been in business for 20 years.
I was never privy to the numbers, but I know carrying the salaries is a huge burden. As a user, proprietary software will often lag off the shelf features by many years because the teams are smaller and they're focusing on things off-the-shelf doesn't do. That's assuming it's well managed.
On the user side of video content: I'm not the biggest fan of YouTube, but bespoke websites can often lack features that keep me from sharing content (wont work on phone, preroll gets stuck, can't link to timestamp). SNL used to only host clips on NBC.com which I could never get to work. They started serving them on Hulu, which was only slightly better. YouTube has been significantly better.
The focus is always spending time/money on the unique thing your company can provide. In addition, like you're saying, be aware of owning as much as possible of your stack--but spreading yourself too thin or trying to run your business the same way you did 10 years ago can bankrupt you, too.