I'm a mechanical engineer, product designer and technical leader that has designed many products, some of which have been implanted in people and are in the Smithsonian, etc. I know screws can come out, that's why they make loctite.
What I'm saying to you is to make sure something is an actual problem before saying it is. In this case, the fact that the screws are used as self tapping, the screws themselves create the threads, likely combats this. Like a nylock nut.
This isn't what I would do for say, a surgical robotics system, but that's not what this is.
If given the choice of having the design as is, or making it more expensive, more difficult to assemble, and less accessible. I'd choose it as it is.
There are always tradeoffs. I believe the designer made the right ones here.
You would be surprised how many screws will go lose after a a thousand of hours of operation, even in this case.