You literally responded to a guy citing Lars Blackmore, who is the engineer that designed their landing algorithm--which was developed at NASA's JPL lab (before SpaceX existed).
Musk bet on landing rockets _because_ engineers told him that it was possible.
In fact it was one of the reasons red dragon was cancelled.
The group studying hypersonic retro propulsion of boosters at NASA was let go because that's what SpaceX did to land
https://arc.aiaa.org/doi/abs/10.2514/6.2005-6682
Lars and Beschet wrote their groundbreaking paper on lossless convexification of the powered descent problem at JPL before Lars went to SpaceX:
http://www.larsblackmore.com/CarsonAcikmeseBlackmoreACC11.pd...
And I don't see any rocket actually coming back with an orbital payload? Where's the demonstrator? Like that quiet supersonic thing Lockheed is demonstrating.
Even Lars didn't deliver at the first attempt. So it's not like it was something available off the shelf. Like some cryptography library you include in your code.
https://ntrs.nasa.gov/api/citations/19980237254/downloads/19...
Those were still winged boosters, but were not helicopter-caught and did RTLS.
Musk didn't invent the concept.
I know only one company landing orbital boosters.