The 1D series exists for a very particular group of photographer. The idea that it's the best camera Canon makes is only true to the extent of build quality, speed, and perhaps low light and button customization. It doesn't mean it's the best camera for you or that you should even consider it just because it's the 1-series. If the features it greatly excels at are something you need, the 1-series is for you. If you don't, look elsewhere.
I personally find myself on the fence of getting a 1-series each year, and talk myself out of it. I shoot a lot of motorsports and think the 1DX2 would kill it for me, but my magazine clients probably wouldn't even recognize the improvements over the 7D2 files I'm turning in now. If I saw myself shooting more sports, guaranteed I would. If I find myself in increasingly harsh climates, I would.
But in all reality, I primarily shoot automotive magazine features, portraits, weddings, real estate, and motorsports. There are better options from Canon for me, such as the 5D3, 6D, and 7D2 that I'm using now. If I bought a 1DX2, it would replace/demote my 7D2 for motorsports only and not replace my 5D3 for its smaller size I enjoy for 90% of my work or the WiFi and lightness I love in the 6D for real estate and travel. You'd want a $6,000 camera to be the one to make you the most money and I don't see that being the case right now for me.
That said, I'm really considering a 5DSR if the 5D4 doesn't fit the bill for me.