People used to get from point a to point b using a horse and carriage too, however, I don't want to do that, I like getting to work in under 15 minutes.
People used to manually focus all their lenses before there was an AF system. That would be horrible in today's rushed society. Again, nothing I want to go back to, I used to shoot with an AE 1, yikes.
People used to have to go buy film at the store before a shoot, then roll the film into the back of the camera, take shots, roll the film back, put it into a canister, load another, and during the entire event, hope for keepers. They had to then send off the film or develop themselves, to get the prints out. Again, nothing I ever want to go back to.
Technology and features/functions/performance advances. Do we "need" these bells and whistles? No, we can get along without the improvements. But why would you not, if funds don't stop you? As others have found out through the ages, these features just help you gain access to and take shots of situations previously difficult or impossible. Liveview, touchscreen, high resolution, high ISO, etc are all enhancers to the craft.
The 5D4 is one of Canon's all time best well-rounded cameras. The evidence is in how many people are still migrating to it, and it is being used as a comparator to others, 2 years after its release. Depending on what you shoot and how much you value your time, the price delta may very well be worth it. One can get a 5D4 for $2400, so $1500 over a 6D may very well be worth it for many.