However, making these things shouldn't be based on class level but skill. That's both realistic and in keeping with the standard rules of D&D. I think it needs something to keep another from dipping, but that solution doesn't set well.Given how the number of times a chemist's abilities can be used is limited only by availability of components and the time it takes to concoct new brews, while a wizard or sorcerer can only disintegrate things a couple of times per day, I would not consider this that big a drawback.
It does give a specific limit. You can sense out to 20 feet.The fact that echolocation is a real and known thing does not mean that one can learn perfect echolocation just like this. It would probably be better fluff-wise and possibly in terms of balance as well if it would have an upper limit to how much space this ability can show to be empty or not.
You have a point, however, considering he also has tremorsense and a sort of echolocation, he has also, over the course of becoming one of the highest level beings in the world, discovered something about pressure points of all structures and can apply his knowledge to match it.So? The class describes a person who has incredible aptitude to structural engineering and chemistry, by virtue of which he or she can bring down buildings. Having similar knowledge regarding the biology of various types of being, including even outsiders, is very far fetched. Surely you do not think that all engineers and architects in the real world have an acute knowledge of the pressure points of a human body?