Belfast shop-owners faced a 15% drop in trade if unrestricted development at Sprucefield had been allowed, the environment minister has said.
Almost one in four shops in the city are already empty and other regional towns and cities could also have lost out had not precautions been taken to protect them, Alex Attwood added.
The developers behind the John Lewis store at Sprucefield near Lisburn have withdrawn a planning application expected to create hundreds of jobs after Mr Attwood decided to limit the type of goods sold at the store to bulky items such as furniture or white goods.
Mr Attwood said Greater Belfast retailers should not be left to sink or swim.
“That is not sustainable planning, that is not good planning, that is not consistent with good government, it is not consistent with good policy and that is why I gave the advice to the planning inquiry in respect of Sprucefield,” he said.
He has faced strong political criticism and First Minister Peter Robinson accused Mr Attwood of using a “Belfast First” policy, warning the Stormont Executive could step in.
He claimed the environment minister was trying to ensure that if Belfast could not have John Lewis, nowhere else in Northern Ireland could have it.
But Mr Attwood told the Assembly the entire region came first and said he had adopted a precautionary approach to protect towns and cities.
“It is the express policy of the Regional Development Strategy (RDS) and it is experienced in other parts of these islands and around the world that in order to drive an economy forward you need a thriving, vital, vigorous city centre,” he said.
“Given that Northern Ireland’s capital is Belfast, are we going to send out the message in a situation where we have 23% vacancies when it comes to shops in Belfast ... that you are going to be left on your own, sink or swim?”
The Sprucefield plans, which include 19 retail units, were to have been considered by the Planning Appeals Commission (PAC) in March.
The consortium behind the plans said uncertainty over planning meant they “cannot proceed to inquiry”.
The application was made by the developer Sprucefield Centre Ltd - a joint venture between Australian property firm Westfield and local developer, Snoddons.
Mr Attwood has confirmed a new area plan would limit further development at Sprucefield.
Last week the consortium, which said it had been committed to investing more than £150 million in Northern Ireland and creating more than 1,500 retail jobs, withdrew the application and cited the minister’s decision.