He actually interviews people who know what they are talking about and does the research. He has good contacts in the industry, better then most people. The video actually contains lots of information you can't find anywhere else. He spends a lot of time validating his videos himself with industry expert and then has a huge patreon community that goes threw everything and tries to find errors.
He is an educator he doesn't have to be able to design his own engine to make good educational videos.
And Scott Manley is also not an engineer and Scott Manley actually used Tims graphics in his own videos.
Right now he is working on a 1h 30min video on Russian engines that is more detailed then anything out-there and he spend 2 years researching it.