Though I think D3 has become a great ARPG in it's own right, you're absolutely correct. 100% inarguably, Diablo 3 will never be what many/most of us had envisioned so many years ago.
I remember damn near trembling when they first announced D3 was officially in development, because I honestly thought they would never do it. But I had no idea they would vary so wildly from D2's formula.
They had a clearly defined starting point with D2, a clear path to continue down. But egos got in the way, and they chose to take their own path. The result was about 2 years of scrambling to figure out how to fix the hot mess that was D3 Vanilla. But....the path they chose will never truly merge with the path they could've chosen, the one provided by D2.