Pretty much every NASA engineer that has worked with SpaceX has been incredibly impressed by their methods. Literally every single one of their competitors, including nation states have started to change their who launch strategy because they saw no other way to compete with Spacex (and they are still failing) all of them have expressed how impressed they are with SpaceX.
You also seem to have a very trivial understanding of what SpaceX is doing and how it is different then what has been done before.
SpaceX is not just developing a the biggest rocket ever (double Satrun V lift-off thrust), or just the most advanced rocket engine ever, or just a new method of landing (very different from Shuttle), or a new type of heat shield (again different from Shuttle or SpaceX Pica), or a method of mass producing rockets. They are fully vertically integrated and they build and work on all of these and many other things at the same time.
Having one prototype explode is fine, because they are not just testing the prototype, they are testing the production of the rocket and optimizing the operations and everything mentioned above. The goal is to have the most advanced rocket of all time by a long margin, and be able to produce it cheaper then a current generation rocket, and operating it as cheaply as a airliner.
You can not simulate or plan anything so complex and get it right the first time. They are constantly learning and improving every single aspect. The engine team uses every test fire for new inputs and adjust their simulation and improve the design, the engine manufacturing team is trying to improve the cost per engine and the production quality, the rocket manufacturing engineers are constantly improving the way the rocket is built and later prototypes have these improvements, the materials team invents new materials and is measuring their performance on the prototypes, the operations team is trying to reduce the amount of work it takes set up a launch and I could go on and on like that.
Literally every prototype coming of the manufacturing line is a incrementally improved and usually cheaper then the one that came before it. The current SN8, SN9, SN10, SN11 are only small differences and with them they want to test the landing. They will be museum pieces once the landing is done, them blowing up generates real world data that can then improve their simulations. One of SpaceX core believe with this project is that the manufacturing system is 10-100x more difficult then the design of the rocket itself, and that their goals can only be achieved if these two things are co-designed. A test of a prototype is not just testing the design but also the manufacturing and quality control.
When you try to design something that has never been done before and is incredibly complex, and you have the requirement that it must be incredibly cheap and incredibly reliable there is no way you can simply design it on a white sheet of paper, simulate it and then simply have a mass production system of that vehicle. That is simply impossible.
And your claim that this is just 'cash burn' for no reason is equally wrong. SpaceX approach to engineering has routinely beat everybody in every single competition and usually by quite a lot. Nobody knows better how to develop something with a small budget compared to SpaceX. The whole Starship program so far, including new revolutionary engines, has cost less half of the much smaller Ariane 6, or less then a single year of the SLS program.
SpaceX is simply universally acknowledged as the most advanced rocket company in the world, and its not close. They are doing it this way for a reason, and they are a lot smarter then you.