There are some fundamental differences, which meant that initially mirrorless cameras were at a disadvantage, but that has started to turn into an advantage the

There are some fundamental differences, which meant that initially mirrorless cameras were at a disadvantage, but that has started to turn into an advantage these days. Autofocus SLRs, digital or analog always focus via phase detection. This was done with a separate sensor module behind the main mirror, which has some transparency. This system can not only detect the exact focus, but also how far the camera is out of focus. This allows the cameras to directly tell the lens where to go in one big step, so focus this way is very fast. Mirrorless cameras of course couldn't use that separate module, so they used "contrast autofocus" where the camera moves the lens and with the image sensor watch the contrast of the picture improve until focus is achieved. Initially this was very slow. But in the meantime, sensor readout and signal processing got much faster and lenses have been constructed, which can change their focus position much faster than traditional autofocus lenses. As a consequence, a good contrast auto focus is a fast or faster as a decent phase auto focus. More recently, phase detection systems were integrated into the sensors, giving the mirrorless cameras the best of two worlds.