Let someone build it for you. the benefits are enormous, and the pc will last you way much longer when you have a self built pc. Medion and all other manufacturers use low end piece of crap motherboards, PSU's and cables, as no one cares about them.
Yes, you are definitely right. In the past I would not hesitate, but also I would not mind buying a complete package, with a steep discount (e.g. with 2 RX480s in crossfire). I get the impression that you are more likely to get a steeper discount when you buy a bulk of products together than if you buy the parts separately and build it yourself. I am sure that the builders are getting big discounts too, which hopefully the can pass (at least partly) down to the consumer.