Sounds like a little competition is required.
Berlin Airports controlled 3 airports:
Tempelhof - a business or city airport which could have survived and operated in the London City commuter niche. Unfortunately, it has already CLOSED.
Tegel - home to Air Berlin, and regional base for Lufthansa Group. BURSTING with little new investment due to the 'imminent' opening of BER.
Schonefeld - former GDR building which turned into a LCC hub for Easyjet and Ryanair (and previously Germanwings). BURSTING with little new investment.
And of course, the sleeping White Elephant.
With private competition rather than local political interference and a monopoly position, Berlin like London could have had 3 independent competing airports offering differing products for alternative markets. Alas only 2 airports remain, but if Berlin Airports were forced to sell Tegel to a private operator, the cash gained from the sale may eventually push them to finish and open BER.
BER would then become a hub for network carriers, offering long-haul connections.
A natural home for Air Berlin and LH group.
TXL would then remain open, run by a new owner and offer an alternative product focussed on short-medium haul routes.
As to which airport would become the base for easyJet, Ryanair, Norwegian etc would be subject to competing commercial agreements. As is the case with LHR, LGW, STN and LTN.
I'm amazed that free market competition can still be stifled within an EU country.
But then again with ADP controlling all Paris Airports, ANA controlling all Portuguese airports, AENA controlling all Spanish airports, perhaps a free market isn't what Europe is about these days. Little seems to have changed from the days of the GDR.
I'm not totally convinced by the idea that competing airports is the panacea for all ill - if anything it drives costs down, largely through under staffing and an over reliance on the "shopping experience".
I can't see that the competing airports in Southeast England has done a great deal to improve passenger satisfaction, or to resolve the capacity problem there.
BER is undoubtedly a disaster, but I can't see that breaking the monopoly of ownership / operation would have made a fat lot of difference - better planning (something that in general Germany is good at) would have done the trick.
Competition (sic) between airports is nonsense, even in southeast England. It has done nothing to provide adequate capacity, so airports specialise rather than compete. Carriers compete (up to a point), airports don't.
LHR specialises in legacy carriers, short and longhaul routes, cargo, premium pax that the carriers all crave (so are prepared to pay millions for a slot pair);
LTN specialises in no frills carriers, holiday flights and charters, mostly shorthaul;
STN specialises in no frills carriers, holiday flights, charters, mostly shorthaul, and cargo ;
LCY is a niche airport mainly serving the London business areas (The City and Canary Wharf), all shorthaul except JFK.
LGW is a mixture of the above and functions as LHR's waiting room.
The result is almost no competition, the airport used depends on type of carrier, type of journey and destination. For real competition to exist, there needs to be excess capacity so that supply exceeds demand, giving punters genuine choice.
This is clearly not the case in London, nor would it be in Berlin. Note the comments about TXL becoming a home for no frills carriers under Berlin "competition", it sounds more like specialisation.
"competition" is also an illusion in UK railways, and in the UK gas and electricity markets. Also, before getting all "gung-ho" about privatisation, please be aware that privatisated airports are very much the exception worldwide. Maybe ask why this is the case.