Is it really that much different than e.g. a cook preparing carrots while onions are being cooked? Nobody needed to invent this as far as my knowledge of history goes; so, maybe there really is nothing new under the sun :)

Joking aside, of course, the ingenuity lies in finding a fitting solution to problem at hand, as well as knowing how to apply it.

Actually, it’s just obvious when you design the most basic ALU and the circuits for doing the carry.

Pipelining requires inserting extra (costly) flip-flops and intuitively one might think that this would decrease the performance. It is not that easy.