From my (new to the hobby) perspective. a bit of both. MTL is quick and dirty and often breaks things in it's nonsensical word salad fever dream output and editing it can range from tedious to tedious nightmare.
Proper manual translation requires a working knowledge of both source and target languages, and at that point, you start to understand that syntax and sentence structure (not even going into colloquialisms, idioms and other turns of phrase that you might find...) is almost entirely different from english, so direct translation needs to be finessed to make it understandable.
And then you get slang, and idioms, and metaphors, etc. where things are not to be taken literally, so you have to choose between keeping the original, but have it come out as nonsense in english, or figure out a good alternative, because it's not just a set of words but an entire unsaid context.