This is again more circular logic. The argument was that 5e dragons as written are not powerful enough, with the evidence being in 5e a town of 1000 people would kill a dragon with 300 people shooting longbows. The same rules however don't provide for that happening on their face. So to prove your point, you alter the stats of the population listed in the rules to be able to do the thing you claimed, as opposed to use the very rules as written that you made a claim about to examine if your claim is true.
What rules? 5e has no rules on populations. This is what the DMG says.
"Consider the following questions as you create any settlement in your world:
• What purpose does it serve in your game?
• How big is it? Who lives there?
What does it look, smell, and sound like?
• Who governs it? Who else holds power? Is it part
of a larger state?
• What are its defenses?"
So the DM decides the defenses, which include militias and their weaponry.
"The guidelines in this section are here to help you build the settlement you want for whatever purpose you have in mind."
The guidelines(not rules) help the DM in achieving what he had in mind. They do not govern and the DM is changing nothing if he does not do things the way the DMG suggests.
The DMG suggests this about a population of 1000.
"Defense: The reeve might have a small force of soldiers.
Otherwise, the village relies on a citizen militia."
Good grief. It even suggests what I have been saying. Militia! I'm not even changing the non-rule suggestion. What is it that you think I've changed?
Look my man, you can alter a dragon too. But we're not talking about altering the rules. We're talking about what they say right now. And right now commoners don't have proficiency with anything other than a club and are described as the overwhelming majority of professions found in an ordinary town. That's it. You can't alter them to make your point any more than I can alter the red dragon to make my point.
Militias don't use clubs. Where are you getting that from? As far as I know, 5e hasn't produced a militia stat block, so I'm still altering nothing by making one. Hell, looking at the bandit, no proficiencies are listed. So bandits can't rob you with anything but clubs, right? Berserker? Nope. No listed proficiencies in their stat block, either.
Similarly commoners have no proficiencies listed, and that stat block fails to include militia members, so it doesn't apply in any case. It would apply to non-militia members of those professions. Hell, would you or anyone else think that a DM has suped-up a commoner merchant by giving him a dagger? No. You'd hear no cries of, "But he's a commoner and can only have a club!" from the players at the table. I could even give the merchant a sword and no one would bat an eyelash.
NPCs are proficient with whatever you equip them with. They don't use PC rules. Arming a militia with spears and short bows isn't changing the guidelines on NPCs, villages or anything else.
Here are the MM guidelines on weapons on NPCs.
"Assume that a creature is proficient with its armor, weapons, and tools.
If you swap them out, you decide whether the creature is proficient with its new equipment."
So even going by the guidelines provided, I can use the commoner statblock and just give them shortbows and decide proficiency, without suping them up. But again, there is no militia statblock provided and I'm talking about militia members, not commoners with no militia training.
You want to sup-up the townsfolk in your game? Cool. Just don't complain when I sup-up the dragon in response. But the 5e dragon beats the 5e town as written in the rules.
I haven't increased them at all, though. Hell, I just decreased them. I reduced them from longbows to shortbows!