The more I read foreign translated articles and books about strength training and the more I get to talk and interact with a few foreign coaches, the more I see a different paradigm when it comes to endurance training.
In the US, I predominately see a go further attitude. Other places it's a go faster attitude. Time and time again, for example, I will get a patient in that wants to run their first 5k or reach 40 miles in a week. They may have some setbacks, but eventually they reach their goal.
What happens next, I've observed, is quite interesting. Predominately, most will then say, I want to do a 10k or hit 45 miles next. I've had very few people say, I want to run faster.
Here's the thing, you can go further, without really getting better as a runner. You cannot run faster without getting better as a runner. To run faster, you have to get stronger, get more energy efficient, improve biomechanics or some kind of combination.
Now I didn't say you wouldn't get better if you ran further, but it's not guaranteed. Run faster though, it is guaranteed. So go get faster!