Well if one wants to uses Rangers long range they combine excellent defensive properties and allot of fire power with 3 bars.
0.8 target size (to 0.57 vet 3), 0.9 damage reduction and with 3 bars around 30 DPS at range 35.
For comparison Lmg paras have around 25.2 DPS and that is without counting the extra DPS from BARS scattered shots.
Ranger +3 BARs should are probably better than LMGs paras.
Keep in mind Ranger will start dropping weapons if they have all slots taken after losing 2 models.
In my experience riflemen are tanky enough lategame, I'd rather have something that can wipe squads. Longrange units aren't designed to wipe. Better to have riflemen that are pretty good at all ranges while the rangers focus on close-mid where they are wipe machines. The thompsons are also good up to mid range, they have more dps (discounting focus shots) up until range 20. It is a bit map dependent of course.