It comes down to who are the better archers.

The fact that longbows can target 600 feet away means nothing else is really going to be very relevant on the field. Sure there are going to be some engagements with heavy cover that can be used to fortify a position, but those guys under heavy cover are basically locked down by the archers. Nighttime only does so much to fix this problem: while many spells simply cannot be fired without being able to see the other guy, ranged attacks have no such complication, they have to "guess" where their target is, and one-on-one that's a great prohibition, but for two forces of 1000 men much less so: the archers all simply "guess" a different spot on the battlefield. And this is supposing the fighter-army doesn't have drow night-scouts ready to light up the other guys with faerie fire if they spot them leaving cover.

In actuality, night actually helps the archers because of the stupid way vision works with advantage and disadvantage. The advantage the archers get from attacking creatures that can't see them cancels out both their disadvantage from attacking something they cannot see and the disadvantage they get from attacking at long range. Plus any other sources of disadvantage they might have. The archers are better at hitting targets when they can't see them.

War clerics have been mentioned here, and you could get more mileage out of them by making half the army Forge clerics who supply them their weapons, for +1 to attack and damage, plus bless on everybody. It's a pretty strong contender. The forge guys form a tight front-line and give the war cleric archers 1/2 cover while the war clerics fire their +1 longbows at the other guys, rolling an extra d4 on the attack roll. And hell, since only 1/3 of them need to cast bless to cover the entire army, let's go ahead and have all the war clerics casting Divine Favor on themselves. Without it, one hit from a longbow is unlikely to kill (due to max HP at level 1), but with it, it becomes a distinct possibility. And killing even a handful of the other guys in round one when you take zero hard losses yourself is a massive benefit.

Cantrips: Clerics can do things like casting Light on the arrows for their first volley to light up the whole enemy army, again that whole "nighttime counters archers" thing is silly. Guidance means that the clerics will have more of their guys winning initiative. Even Thaumaturgy, for communication on a battlefield, is a significant boon.

Fighters are interesting at first glance because the fighting styles allow for what is effectively a phalanx formation via the Protection fighting style, but this falls apart once you realize all Protection does is assign disadvantage... which we already have, because the bulk of combat will occur at 600 feet and possibly at night. The archery fighting style's +2 to ranged attacks is outclassed by the clerics' +1 weapons + bless. Fighters' extra 2 HP is taken care of and then some by those same +1 weapons and Divine Favor.

The clerics will obviously beat out the fighters on healing: Second Wind is self-only and can't be used to wake up a fallen ally. It heals an average of 6.5 compared to a cleric's

Clerics win on logistics too: they can cast Purify Food and Drink and Create or Destroy Water, which isn't quite as useful for this purpose as druids' Goodberry but it's better than the fighters can manage, which is entirely reliant on the ability to live off the land, which isn't going to be easy if you're pinned down behind cover and under siege. You can help mitigate this by using Warforged as the bulk of your forces, but that leaves the clerics free to pick wood elves or centaurs or catfolk or some other highly-mobile race.

The idea of wizards being able to sneak around and infiltrate enemy forces with any kind of reliability is silly, not when you've got a force composed entirely of guys with +3 wis, insight proficiency and guidance on tap. The rogue army, with expertise in deception along with a race like changelings who can actually infiltrate worth a damn? Yes, absolutely they could pull it off, but not wizards.