The real problem would occur if you had to stop or slow down as quickly as a car that actually had real brakes, like say an AMG. But hey... it would be HUGELY hypocritical of me to say that you should Not have done that.
In a situation when you completely lock the wheels, you're trading the friction between the brake pads and brake discs, for the friction between the tires and the road surface. In other words, instead of the hydraulic clamping force on the discs, you're relying solely on the weight of the car. The interface between tire and road is not nearly as good as the interface between brake pads and brake discs, which wear to match each other exactly, as they're used.
So as a good rule of thumb, you never ever want to lock up your brakes. That's why anti-lock brakes are standard.
(The main exception is when driving on relatively deep and loose surfaces, such as sand or deep snow, where a locked tire builds up material in front of it.)
Undersized discs and pads have less thermal capacity, so they will tend to overheat and lose braking ability. A lot of lower-spec and economy cars will be perfectly capable emergency braking from full speed once, but you absolutely have to let the brakes cool off afterwards, especially if it has unventilated discs and rear drum brakes. That's fine, as long as you're aware of the limitations.
In comparison, a larger midrange car (such as a VW Passat) can reasonably handle repeated emergency braking situations without losing any significant amount of braking power, thanks to larger discs and pads.
There is also the matter of pedal feel, how confident the brakes feel or if they feel mushy and imprecise, and how the ABS system works.
So yes, of course the contact patch matters, but only if the brakes are adequately capable.
Locking your brakes is not the fastest way to stop. What you want is to apply the maximum friction to the road, this means your brakes have to be letting the disks travel, and at very high speeds your disks and callipers get very hot, very quickly, at which point they stop supplying nearly as much stopping power, and you might in fact no longer be able to lock your brakes.
Anti-lock brakes (ABS) are an improvement, because they mean that if you over-brake (locking your brakes) they release them until the wheel starts rotating again, before re-applying the pressure. They're better than locking your brakes, but they're actually less effective than holding your brakes at the optimal pressure. They're just a lot easier to use than it is to apply that pressure manually (particularly as the optimum pressure changes as your speed does and the heat of your disks and callipers).