I would not say that only one is the right solution, it depends what you film. For fast handheld, dynamic, running shooting - monitor s the only option, but for concerts, especially where light are going all around or outdoors when sun shines on your back - viewfinder does much better. Both cases - higher the resolution easier to get focus, but remember that most canon dlsr cameras drop the hdmi resolution down when recording, except 7D, 5Dmk3, 1DmkIV, 1Dc, 1Dx (correct me if I have missed one), so in case you have a camera that drops the resolution while recording, then high res monitor is not that useful.
And you don't judge exposure from monitor, or any other type of screen unless you have loads of money for high end stuff and have calibrated it, tough you probably would not shoot on dslr then either. You use zebras, histograms, waveform monitor, vectroscope, even a light meeter, but not you lcd screen in camera or external. It lies, badly.
on focus ML brought som egrate features like Digic peaking, and focus assist as such - really helps, takes some getting used to, especially if dslr is your first video camera. for me - I started with ENG, and other shoulder cameras and I'm used to have those PRO features, moved to dslr only because of the price/performance ratio and the type of work I'm doing. And because of ML brigs pro features.
