If big unit with single target weapon is fighting small units, consider the TTK for the large unit compared to the number of smaller units:

Cloakraid has 230 hp vs spiderriot's 70 dmg every .3s (1.2s TTK) -> 6s TTK for entire group. Range of 300, speed of 54 vs 116 speed (diff: 62/s), range of 185. Consider each glaive starts at range 300 and must cross to 185. This gives redback 56 frames of free engagement (1.86667s) in this time redback will score 1 kill and be ~50% towards a second kill. At 2.4s into the engagement, a second glaive will be lost. At this point the glaives will have dealt ~226.8 damage to the redback out of 900 dmg. At 3.6s into engagement another glaive will have been lost during which the three glaives will have dealt 378 damage to the redback for a total of ~604.8 damage. At 4.8s a fourth glaive will have died during which the 2 remaining glaives will have dealt 252 damage for a total of 856.8 damage. With only 43.2 hp remaining the redback will be killed in less than 0.5s. This assumes perfect engagement (ie: glaives do not bodyblock), in other words the only way 1 redback can win against 5 glaives is through an error occurring that costs the glaives up time while suffering no uptime loss itself.