I have a difficult time seeing how this is possible with such low stats in 5E.... Care to elaborate with a specific example or two? I am sure it's possible, but off-hand I am not seeing it.
In short, the other players sucked at the (tactical part of) game.
<edit> Hard to remember specifics because I’ve given up caring about that specific campaign, but an example I do remember:
We were about 3rd level and surprised some gnolls in the jungle performing a ritual. As my first action, my monk ran/jumped up a nearby tree And got out his bow. The (Dragonborn Eldritch Knight) fighter charged directly into the five or so gnolls, waving his two-handed sword (and 13 AC)*. The Druid did what she always did - Poison spray or thorn whip a gnoll. The bard inspired ... someone.
The gnolls then proceeded to wail on the fighter, though the DM was kind enough that when the 3rd one had dropped the fighter to 5 hp, the other two moved off - one against the Druid, the other after the monk (instead of the bard on the ground). The latter gnoll had a bow, and took a shot at the monk, and I promptly used Missile deflection to negate the damage and shoot the arrow back at him.
Next round, the fighter continued battling (had to remind him he had Second Wind), the Druid healed the fighter instead of attacking (taking an attack of opportunity to evade the gnoll attacking her), the bard mocked the gnoll that had been attacking the Druid. My monk put an arrow through the Druid’s gnoll, killing it. On the gnoll’s turn, one attacked the fighter (and suspiciously missed), another the Druid, the third moved from the fighter towards the bard, and the last remaining spent his action climbing the tree towards the monk.
Next round, the fight continued as the previous round - fighter killed a gnoll, Druid healed, the bard poked his gnoll with a rapier. The monk used a flurry/way of the open hand and ended up kicking his gnoll out of the tree, killing it.
After the gnolls Attack, the monk moved down from the tree to engage the gnolls by the fighter, managing to flank and knock at least one down, so fighter could hit and kill the downed gnoll (the fighter was getting some crappy hit rolls that combat).
The rest of the fight was wearing the gnolls down - monk knocks them down or away from melee so the non-fighter characters could use their ranged cantrips (or the Druid use a Cure Wounds on whoever got hit) and wail on the target until dead.
* The fighter ran directly into melee, despite having a bevy of ranged attacks (and us noticing only one gnoll had a ranged attack - with our original plan to snipe them and force them to come to us) and without taking the time to cast any of his pre-combat buff spells.