Both didn't start with PoS because it's much more difficult to come up with a practical PoS design than a practical PoW design. I consider Casper CBC to be the

Both didn't start with PoS because it's much more difficult to come up with a practical PoS design than a practical PoW design. I consider Casper CBC to be the first robust PoS design, and it took many years of research for it to developed. Look at peercoin for an example of an early PoS design that was fundamentally flawed. PoW was ready back then, PoS tech was not there yet.