The corporate office where I work has many meeting rooms with projectors or TV screens. Typically there are two connectors wireed to the meeting room table - VGA d-sub and HDMI. I will never get the time back which I have spent watching presenters faff around with getting their display working.
More generally, the problem for the device owner is to have a connecting cable which will work with any foreign display they need to present on. I'd rather use DisplayPort myself, but the most commonly available digital port is HDMI. The sad reality is that USB-C HDMI output is going to be the most frequently used display output from next generation devices.
MHL uses the same physical connector as HDMI (at the display end) and the average punter isn't going to know if a given display supports MHL. I forsee that in the future, people will have the same problem with USB-c connections. They same physical port supports so many display standards that people who don't read the manual are going to become frustrated figuring out which ones are suppoted on a given device.
Ideally, I would like to see some sort of wireless display standard that's easy to pair and widely adopted, but that's not happening any time soon.