So then the answer is yes, they can break down the door, so the halflings are not fortified.
Man, this is some dangerous frontier they live in. Gnolls that replenish from a single gnoll, and always come in with perfect tactics and perfect knowledge of ranges.
How fortified any given settlement is is proportional to the expected threat.
The question is not whether halflings can drive off raiding parties. Clearly they can or the village would not be there. The question is twofold. How can they - and how is that different from how humans would do it as halflings are not actually humans except at the same level elves are? Both have been answered.
Actually... the gnolls are just following the lore in how they replenish. That has nothing to do with anything. Their "perfect tactics" involve... shooting arrows or throwing spears at people they can't stab, and not just running through a hail of sling-stones and dying without hitting anyone.
And the people with perfect knowledge of ranges seem to be the halflings who are always 30 ft away before firing their slings (and being able to move back 30 ft, since they aren't going to end up in melee)
And, I actually answered that question of how can they drive off raiding parties.
They have crossbows, and have trained a bit in how to fight and drive off gnolls. My only complaint was that slings are an inadequate weapon for defending a town against a threat. I'd also prefer some more militant things, like rangers or scouts and maybe a wall for the village, but that's it.
I don't - and don't believe it happened any more than we have a maze in the streets rather than shaped hills that provide corner, and some obstacles the halflings know to avoid.
Shaped hills? So, they just have windy streets? And the gnolls can't run over the hills and ignore this sudden cover because....
Look, this isn't that hard to get right? Slings just aren't a strong enough weapon with a long enough range. The rest of this is stuff that can potentially work, maybe, but not if the halflings have to be withing 30 ft. A Light Crossbow takes them from an average of 4-5 damage (assuming your +2 dex mod, which I'm just giving you at this point) to an average of 6-7 damage. That is doubling their damage. And their range is massively increased. To the point where the gnolls can't throw the spears at them, and they would need to rely on the bows. Which does make it incredibly dangerous for the halflings still, but gives them a far better fighting chance.
And that is it. That is the miracle I am asking for. Better weapons than a sling, which simply isn't going to cut it against dangerous enemies. Maybe they carry the sling for personal protection while traveling, or in the city, but if you are talking about defending the town from a raid? You need more than slings.