Unless I'm mistaken, port injection was added to the 3.5L Ecoboost only, not the 2.3 or 3.0L. Also, Isn't the waterpump internal on all FWD based Explorers?
If I were to get a '11-'19 Ford SUV, I'd look at the Expedition instead, look for a V8 2010 Explorer, or wait until I could afford the 2020 Explorer.
Now, there are a lot of people who drive the 5th generation Explorers with few problems. I'm sure maintenance is key. Keep up with oil changes, use full synthetic oil, check the pH of the coolant and change at regular intervals, install the catch can as suggested, always use a top tier gasoline, and you will have fewer chances of having issues. Of course, the problem with buying used is that you have no idea how it was maintained before. If the previous owner lies about maintenance and you buy a lemon, your stuck. I suppose if you buy from a Ford dealer and get an extended warrantee, that may help.
I liked the idea of the Ecoboost, but not until they added the port injection in there. Only time will tell if they add the port injection to the other Ecoboost engines as well.