The strategies haven't actually changed... I just relabeled them in anticipation of adding Antorus gearing strategies.
I meant to use something a bit generic... still going back and forth on how to label them. I'm not quite sure which M+ levels they will correspond to after they retune M+ when Antorus Mythic comes out (they always up the base difficulty a bit).
"low level" corresponds to doing an M+ that is challenging if you have around ilvl910 gear.
"5-8" corresponds to doing an M+ that is challenging if you have around ilvl930 gear.
So if you pick "5-8" and have e.g. ilvl940 gear, it will probably push you towards DPS-oriented gear.
With Antorus, we'll add one tuned around ilvl940 or so (heroic antorus gear), and ilvl960 or so (mythic antorus gear).