No question they were pioneers in the concept, but personally I give a huge heeping helping of credit back to Northrop.
They created the XB-35 and YB-49 aircraft and had them
flying when the designs were pushing the technology of the day. A flying wing is so hard to control and that was the ultimate downfall of the YB-49. Note that it has small vertical stabilizers where the XB-35 does not.
We ended up getting the B-36 instead as it was thoroughly conventional and more "proven" design. Of course it was already a old plane - just a bigger B-29 in concept. Which is to say only a slightly better World War II type bomber.
The XB-35 had the advantage of using the props to help maintain stability, but the props also held it back. The air-frame could handle far more speed.
XB-35 Flying Wing and XB-36 Film Clips
https://www.youtube.com/watch?v=LOeh_ZDKo4E
You gotta love a sleek flying wing with eight turbojets and a bubble canopy! One of my favorite planes!
Northrop YB-49 "Flying Wing" - Taxing, Take Off & Flight Operations (1947)
https://www.youtube.com/watch?v=kuIFvNA1UgU