also many small files means that you not just send more header frames, also the whole chatty http/2 protocol sends more data. http/2 is chatty and stateful, that's something people should know about. so the best possible outcome is probably do concat, but don't be so aggressive than on http/1 do concat more when you have more mobile users since http/2 does not fix their mean latency and their bad bandwidth
You are right, my statement is not correct. It certainly does not completely negate the overhead of additional headers. It does greatly reduce it though. So far, I have only heard of compression inefficiency being a real problem when not concatenating. Do you have some examples of header overhead actually being a real issue? Would be happy to update the post.