Desk research against primary sources. Figures are traced to the issuing UAE authority and linked on the page.
The AED 200–400 figure is really a float for the handful of situations where a card will not work — a souk stallholder without a machine, a taxi driver who prefers notes, or a small tip — rather than money you expect to spend down over the trip. Withdraw it once from an airport ATM on arrival rather than repeatedly from hotel ATMs, which often carry the least competitive rate of any option available.
The exchange-rate gap between an airport counter and a city exchange house is the difference that actually moves your budget, not the cash-versus-card question itself, so if you are converting a meaningful amount, wait until you reach a city exchange house rather than changing it all on arrival. Cards cover restaurants, malls and most attractions without any premium, so there is rarely a reason to carry more than that float.