I do try to kill the weakest ones first, but sometimes that creates a problem where everyone targets the same mob and it dies so fast that time is wasted in aborted ability activations and re-targeting. In that situation I usually switch to a stronger one for a while. And sometimes I just don't notice all the weaker enemies, or one of them is behind an obstacle and I can't shoot it.
I hope people aren't complaining about the moments like this when you just don't see the right target. or if you have already commited to a target and are burning it down. I am DPS and follow this weak to strong kill order unless there are healers present then I go after them first like a honey badger (like in long shots in section X). Honestly, most of the people that don't follow basic game strategy have never gone online to figure out what they are doing wrong.