From my point of view, the HDMI port exists for one reason. When you enter a random conference room, there is usually a HDMI cable waiting. You are expected to plug your laptop in and start presenting without wasting everyone else's time.
In my experience, ~2/3 of Mac users do that, because they carry the necessary dongles with them. The rest either forgot it or rely on finding one in the conference room or borrowing it from someone else. Sometimes that works, sometimes it doesn't. Because too many Mac users behave badly and thus damage Apple's brand value, the HDMI port is necessary.
Also, it looks like the new MBP has 3 Thunderbolt controllers, while the old Intel models had 2. Because it's always possible to add new ports with dongles, we actually got a 50% increase in USB-C/Thunderbolt connectivity.