Macedonian Sarissa? I’d think people would be using halberds both because it could be used for stabbing and slashing.
That's not how people fight once we're back to that kind of weaponry. In reality, people form blocks of spearmen who are standing virtually shoulder-to-shoulder and moving/fighting directly to their front. The spears form a hedge of points which prevent non-spear-equipped troops from closing with them. Therefore the spear-block pushes them backwards. In the language of the day this was called "the press of the pike" and was
the decisive tactic until musketry came along. The seventeenth century was marked by a steady increase in the proportion of musket-armed infantry (referred to as shotte) until the invention of the bayonet eventually eliminated the pike. The press of the pike was replaced by salvoes of fire to break the enemy line followed by a bayonet charge to repel it.
That's a very brief summary of a complex period of warfare. The point is though that the closely-packed ranks of spearmen didn't have the room to slash with anything nor was it desirable for them to try. Attempts to slash would break up the integrity of the wall of spear-points and bring about an immediate danger of the pike collapsing. Halberds and so on were ceremonial weapons and rarely used on the battlefield. Senior sergeants would have a short halberd called a spontoon which was primarily used to dress the ranks and cut down anybody who tried to run away.
I’d still think that swords would still be a weapon used, if only something that’s not drawn till an enemy gets too close and their spear is gone
Remember those closely-packed ranks of spearmen. they don't have the space to draw a sword and start swinging. Forget what you see on television; battles just weren't fought that way.
Also, modern day metallurgy and engineering, I think would make something better or new
Why? Some things cannot be improved. There's a reason why a 17th century pike is almost identical to a 4th century BC Sarissa. In fact, a 4th century BC Macedonian Sarissaphoros would be entirely at home on a 16th or 17th century battlefield. Improved metallurgy would give his a spearpoint that would be less likely to break but that's all. This comes out in the story The Salvation War; for almost 2,000 years, the human battlefield and its technology hardly changed. The Macedonian Phalanx was replaced by regiments of Pike but the two were fundamentally and functionally identical. It took the introduction of Shotte to break the blocks of pike.
Before you ask, cavalry will usually not break a phalanx. Horses are much more intelligent than humans, they will NOT press home a charge against a hedge of sharp steel spikes leveled at their eyes. The best way to take down a phalanx is to outflank it. (this is what Roman Legions were designed to do).
Considering every combatant would be wearing something like munitions armor with chainmail covering exposed parts, I'd reckon warhammer or mace would be mor useful than a sword. Not that it would matter much as anyone trying to get into melee range would get run over by a vehicle or gassed. Since there is no AA defenses, nothing can stop crop duster aircraft from dousing the battlefield with VX.
This is more or less what happened (excluding the VX bit). When plate armor replaced chain mail, the old idea of trying to bring down the wearer by means of a sword thrust became obsolete. Instead, the use of maces and morningstars, impact weapons designed to crush rather than penetrate became the norm. So I think you're quite right, we'll see the same thing happening. In fact, we are seeing it right now. Body armor is becoming so effective that pistol and intermediate rifle ammunition (for example 9mm or 45ACP for pistols and 5.56x45 or 5.45x39 rifle) are becoming ineffective. So attention is reverting to crushing power and full-power rifle rounds. I think this is what is behind the Russian 9.3mm rounds and the growing acceptance of .338 Lapua.
I saw a demonstration of a modern vest draped around a pig carcass not long ago. 5.45x39 and 5.56x45 were stopped by the interceptor plates with only bruising to the tissue underneath. .45x70 rounds crushed every rib in the pig's chest.
Wait? Modern and Medieval Armor can easily take full strength slashes and stabs? Not what most fiction has shown me.....arrows go through no matter the distance
Lesson for the day. Don't believe what you see on television. Chain mail can be penetrated by a fine point (the sword designed to do this was called an Estoc or 'tuck' and is the intermediate step on the way to a rapier). Bullets penetrate things like Kevlar more or less the same way, they force the fibers apart. Only, modern vests are designed so that doesn't happen. Once plate replaced mail, the Estoc and its derivatives went out for military use.
The primary rule for sword-fighting is that the point always beats the edge. Contrary to popular belief, a rapier used by a skilled swordsman will always beat a katana wielded by an equally skilled man. It's all a matter of reach and speed of response; the man wielding a katana simply can't get past that rapier point. Eventually he'll make a mistake and walk on to the point - which is fatal unless one is plate-armored.
Arrows will bounce off plate armor and are iffy against mail. The English had an armor-piercing arrowhead called the "long bodkin" which was effective against mail (as the French knights at Agincourt found out) but even then most knights were brought down rather than killed (the correct response to a dehorsed French knight begging for mercy is "je ne parle pas Francaise"). The key change brought about by the introduction of shotte was that a musket ball will penetrate a breastplate with a high degree of certainty. The answer to that was to improve deflection angles so that the shotte would be deflected - hence the development of "pigeon-breasted" armor.
. Technically, a block of pike could be anything from five ranks upwards, the actual depth being determined by the forces available and the length of front to be covered. The front rank hold the pike level then each successive rank behind them at steadily increasing angles to form the hedge of points. Now, when we do the maths, we find that (for example) an 18-foot sarissa means that probably only the front three to five ranks can actually contribute to the point-hedge. So what do they do? One things is that they hold their spears over the heads of the men in front to give them some measure of protection from plunging arrowfire. A second is that they provide reserves so that if a man in one of the front ranks goes down, one behind will step forward to take his place and maintain the spear-wall (the Romans were past-masters at that - they actually had drills so that the men at the front could retire to rest while fresh men at the rear would step forward to take their place). A third is that the men behind give the whole formation solidity and stability and push the poor men at the front forward.