Brookyln is not Monsey or Lakewood, It can handle higher density housing
The issue with the other population is why people move to the Suburbs and what they want there. Non-Frum people want lower density housing, they want yards, they want driveways, they want backyards, they want good public schools , good libraries and nice parks. They also want a seperation between housing and non-housing edifices (Like Schools and shuls) on streets. meaning they dont want places of worship on residential streets, they want them on main streets.
Frum people want higher density housing (but less dense than Brooklyn) they dont care about public schools or libraries and dont want to pay for them. Frum people want parks with playgrounds rather than parks with ballfields (Ballfield parks take up more space), so you can see where there is conflict, there really isnt a middle ground