Since I like to test what I say, I started a game near a tower. I embarked with 6 military 1 carpenter/armorsmith and enough materials for steel armour all round.
Owing to the sheer borkedness of melee in this version, I did something I never do, and danger room trained my 6, who had become a fantastic five, because one of them was later found drowned in the middle of a pond. Later a talented macedwarf turned up so I turned them into six again.
Around the second year a siege of undead Minotaurossi turned up. I'm playing Fortress Defense II mod, and Minotaurossi are one of the challenge mode enemies, they are about 5x larger than dwarves and wield weapon and shield, they are trap immune and stuff, basically like the minotaur semi-megabeasts, except a civlization so they arrive as sieges. A single squad arrived.
I dutifully bumrushed the zombie minotaurossi with my fantastic six. After a prolonged battle, in which about half the minotarurossi were killed, all my dwarves were dead. It was a fairly typical failure mode - they passed out from exhaustion and were then killed. This is a fairly typical experience in Fortress Defense II, the sieges are simply so large that your elite dwarves eventually pass out.
Now the challenge mode enemies in FD II, are basically designed to give a player skilled with military, a serious challenge. That's alive, if anything should be able to wipe the floor with military dwarves, it is undead versions.
I suspect that if the dwarf weapon use weren't bugged, they would have thrased the undead minotaurossi, the problem is a fist fight with zombie minotaurossi can only end in one way, so only weapon blows from the dwarves count. If they only use their weapon say, 20% of the time, then the battles take 5 times longer to conclude, and the dwarves pass out from exhaustion. However stun-locking was also a problem, since 5 dwarves were fighting 20 enemies, the dwarves spent most their time stunned. That doesn't seem to affect block/parry/dodge, but it does prevent them dealing damage.
I save-scummed back to the start of the siege with intent to use strategy and examine the behaviour of the undead. First, my soldiers badly needed more danger room time, some of them were barely legendary weapon users. I de-equipped their shields to force them to use their weapons to parry and thus up their weapon skill faster.
The undead minotaurossi basically hanged out at the side of the map. After a while I opened a new passage to the surface (the starting wagon happened to be very near that map edge so the existing entrance was unsafe) and started cutting trees and gathering wood, in more-or-less perfect safety. Over the next few months the undead slowly 'defused', the leader (necromancer?), a living minotaurossi separated from the pack and tried to kill my dwarves so my dwarves killed him.
I used the trick of "staircase channels" to try and lure some of the undead underground into passages. Normally my dwarves would see the undead and flee, before the undead saw the dwarves. I did eventually manage to lure a few undead into a passage, where they were swiftly dispatched by the six. I also dug out some "staircase channels" with intent to partition the undead, with fairly limited success, but at least breaking up their mob further (I did confirm that the frightened dwarves did NOT try and climb out the channels to safety, instead they ran to safety along the actual safe route).
Finally after 2 or 3 months some of the pack of undead defused enough that a couple of them noticed my dwarves and attacked, so I rushed them with the six. 4-5 of the undead had already been killed in the passages, and another 3 had wandered off out of range of the pack, the remaining ones were partly partitioned by the deramped channels, so they only met the six in dribs and drabs. With the six ganging up on only 1 or 2 at a time, they swiftly mowed down the undead minotaurossi and the surface was safe once again.
Now I am aware that undead sieges come in pretty different forms, this was a new one for me. It was atypical of being a small siege, of extremely buff enemies. I'm more used to huge swarms of all sorts of things. But those swarms have always been hell-bent on getting into my fortress.
Essentially though, if a small group of elite dwarves could beat down undead minotaurossi, they should be able to beat anything in vanilla. The two keys to success are then:
1) Attaining ultra-legendary skills so that the dwarves gain total immunity to damage through the use of block, parry and dodge. This immunity only lasts as long as the dwarf doesn't pass out from exhaustion, leading to the second point:
2) Divide and conquer. If battles last too long, dwarves will pass out. This requires partitioning the map, or just letting the undead defuse over time.
One of the good things is that time is on your side, if the enemies don't path into your traps, then you can spend as much time preparing as you like.
The other thing, is that since the undead don't move, and only slowly 'defuse', the interior of the map remains pretty safe for harvesting resources.
The only problem, is that this required outright abuse of danger rooms. I use the danger room barracks (to also get experience from drills and sparring) and had a dwarf on permanent lever pulling duty. Normally I consider danger rooms distasteful at best, but given how broken melee is in this version, I consider them acceptable.