I'd imagine they use kph for two reasons
- They use m to divide and measure the pitch
- So they can compare against European leagues
I see you're relying on the old "stats are flimflam, I know what I've seen and I'll rely on my own eyes rather than some nerdy stats" argument. What's your opinion of people who tend to make that argument? I know I and most educated people have one.
Here are some pointers as to why you appear to be struggling with understanding the stats and why they're correct:
- You've picked the first data point that suits your preconceived opinion and stopped looking. No, Dier isn't as fast as Mbappe - he has been measured at up to 38kph in other seasons (Bale 37kph for reference) but in that season he didn't run any faster than 35kph.
- You've massively overestimated the number of times you'll see a CD run at full pelt in a match. King was one of the fastest CDs we've ever had, and I can probably count on one hand the number of times we've seen him really sprint like he can - probably have a couple of fingers left to type with too.
- Memory is fallible and so is perception. Larger players always look slower because we have an assumption that big lumps are slow and little players are nimble and fast. Most people don't think of Benteke as quick either for the same reason. When it comes to memory, the human brain is absolutely terrible as storing and recalling clean facts. Your brain will use your biases to interpret what it sees as it stores the initial viewing of an event and will often then discard and fail to recall anything that doesn't fit your biases. Even if it can recall that event, it will apply your biases as it recalls it too. That's why we rely on objective measures - to remove these biases.