> Power lifting is a specialization.
Starting Strength is not powerlifting, and strength is a general adaptation. The fact that you do not know this makes me think you haven't read the book, and therefore are not in a position to argue against it.
> Few power lifters can do calisthenics staples such as muscle ups, flags, and front levers.
These are skilled movements and must be trained. If you're stronger, learning to do these things will be easier and quicker. (Since they are ultimately strength-based movements, as are most things, and strength is a general adaptation.)
> So, since the barbell method is not the only type of strength
The only type of strength is to produce a force against an external resistance. That's what strength is.
> Linear progression is dangerous. Within 8 months, a beginner will be hoisting hundreds of pounds in their squats and deadlifts.
Good, that's the goal. Their bodies adapted to the external stresses and became stronger. Now they've grown and are physically capable of lifting hundreds of pounds. How is this a negative?
> Not all of them will have proper form
We're talking about four basic movements here. Anyone that is persistent and possess enough intelligence to read SS (and is young enough) can, in fact, do these movements. Certain cases do need a coach, but that's the exception. (Except for very old people--they seem to require coaches.)
Anyway, I don't really understand your thesis: again, the data is telling: weight training is just about the safest form of physical activity. It's also just about the only form of physical activity that lets you precisely, numerically increase the weights such that you become stronger in a controlled, measured way. If you really believe that doing gymnastics (muscle-ups, flags) is safer than squatting, then you're delusional. (And the data strongly agrees with me here as well: injury rate for gymnastics and gymnastics-like sports (cheerleading) is rather high.) If you believe the physical benefits of doing gymnastics exceeds those of weight training, you're extra delusional. (No incremental loading, the lower body consists of muscle bellies that are just too large to load effectively with bodyweight.)