Hmm guess I was a bit strong but a point had to be clarified. In defence of the train set manufacturer they do deliver a quality product if used as designed. However, like the difference between a Euclid Quarry vehicle and any popular 1/2 ton pickup truck, they're great if used as designed. The quarry vehicle was not meant for the road and the pickup would be useless hauling stone in a quarry.
A lot of fun can be had with a trainset, but the loco was meant to haul only those few cars that came in the set. If a person has visions of building a serious operating layout, that is when the Trainline, & Athearn kits (Low end priced Model Railroad locos) come into play, these units have all wheels for electrical pickup and all axels are powered. In addition they have flywheels for smoother running, are heavier with more powerful motors to handle much heavier loads ( more cars). They also have qualities which detract from their popularity. This is where the next generation of more expensive loco's come into play. They run quieter, have flywheels that are more balanced and in general give a better performance. The next more expensive locos have much better details.
Now it isn't exactly like that but in all it's a general idea of differences in prices. I just had to clear the air for the trainset hobbyists it also is modelrailroading and there is nothing wrong with your trains if used as it was designed for.
My My but I do go on, Also in defence
of the train sets look at the units on my website, the bodies are all from train set locos, however, the frames trucks and motors are all from Athearns.
