The notion of UC(ie a single working age benefit) was proposed in 2009, perhaps before then.
The DWP do make errors and outright sloppiness in decision making, but the examples used in this thread are not usually amongst them. Concentrate on the real errors going on, not the headline ones, which are often false or simply a total misunderstanding of the rules.
Eg Maximus Medical report states "breathlessness on exertion", Hospital and GP also state that, medical reason for it identified(which is important), but not taken into account when deciding anything on the basis of "no breathlessness when brushing teeth".
Lost at Tribunal, but won a rehearing from the Upper Tribunal, but not on any medical basis. I won it on a strange thing in the rules, that is really a physical state of affairs and isn't something that I would have got a medical note from a GP for. Eventually I won the rehearing at the First Tier Tribunal(they stopped it before the end) on the basis of "breathlessness on exertion".
Eg You can't complain about losing benefits claimed under the special rules(expected to die within 6 months), when you're still alive 2 years later. You might still be eligible, but not under the special rules.