In most cases when it is appropriate to use engine braking the person behind you has to already start matching your speed. In situations where you have to brake suddenly and quickly brake lights can warn the other driver, but in most cases when you are downshifting to engine brake you are slowing down slowly enough that the person behind you can make proper adjustments simply based upon the fact that they are now getting closer to you. It's a human PID loop!
As for rev matching, yes, completely agreed, if you can't rev match your down shifts then engine braking is indeed going to use your clutch and that is more expensive to replace. However, if you are driving a stick shift car and you don't know how to properly rev-match on downshifts how will you easily get up the mountain where shifting from fifth to fourth to third is sometimes required simply to keep up with traffic properly? I can go from fifth at 3k to fourth at 5k without issues. Rev-matching in a stick shift is very important outside of the engine braking use case.
As for rev matching, yes, completely agreed, if you can't rev match your down shifts then engine braking is indeed going to use your clutch and that is more expensive to replace. However, if you are driving a stick shift car and you don't know how to properly rev-match on downshifts how will you easily get up the mountain where shifting from fifth to fourth to third is sometimes required simply to keep up with traffic properly? I can go from fifth at 3k to fourth at 5k without issues. Rev-matching in a stick shift is very important outside of the engine braking use case.