Well the idea is that we don't put them all together and generate slum areas, those areas can be a problem not only to the immediate area but are wider reaching. I do agree to a point, but I understand both sides.
House builders will generally agree to the quota then negotiate it down anyway, councils have targets to meet so cave in easily, builders get more profit that way.
Generally, you might find the houses at the front of the estate are a bit better than the last ones. Where cost and schedule got tighter!
Don't discount all new builds. Mine is 2008, on a plot of 3 built to a very high standard by an independent. But yes, the larger companies may cut corners due to budget and schedule.
Personally, I don't like the parking arrangements on the bigger estates for one. There's some good planning points and conflicting ones, but the policy's, local and national are open to interpretation and bent towards the councils targets anyway.
It's a cut throat business.