During World War II, the Japanese issued what became known as "old military" swords (kyu gunto, type 32) and "new military" swords (shin gunto, like the type 94, 95, and type 99). The kyu gunto was based primarily on European one-handed sabers, albeit with a blade shaped similar to a katana; the shin gunto ditched the European design elements in favor of a more traditional katana design. Both styles of weapon had many variants depending on service (army, navy, or a civil service), whether it was intended for an officer or NCO, method of manufacture, and available materials. While some blades were traditionally made (or officers had family blades fitted to new hilts), the bulk of these gunto were mass-manufactured from sheet steel for the blade, and other materials as available for the hilt and fittings. For more technical specifics you can look in the Encyclopedia of Japanese Swords by Markus Sesko - who has written a great deal about Japanese swords (this particular book isn't on WorldCat yet, unfortunately, probably because it's lulu).

As swords, the gunto were technically functional and training with swords was widespread in Japan during WWII, but their use was primarily ceremonial most of the time - every officer was issued one as an indicator of rank. Swords were generally on their way out as a weapon of war, even if they did see occasional use in charges (and cavalry actions, during the Russo-Japanese War). The mass-manufactured gunto were recognized, however, as not being of the same artistic or technical quality as traditionally-manufactured Japanese swords. Japan has relatively poor iron sources and traditional swords overcame this difficulty by pattern welding, where alternating layers of high-carbon (and brittle) steel were folded with layers of low-carbon (and soft) steel, and water-tempered along the edge (producing the distinctive hamon); the resulting blade was usually much stiffer and less flexible than an equivalent European blade, but could have a very hard cutting edge. Gunto blades were generally made from sheet steel and oil-tempered, and as such were much more uniform in quality than traditional katana, but lacked the hardened edge. A decent look at some of the technical details that differ between traditionally made and mass-manufactured Japanese swords can be found in Yakasuni Swords by Tom Kishida.

The Chinese dadao used during World War II was very different in purpose than the Japanese gunto. Chinese officers generally used (as far as I've determined) either European-style sabers (at the beginning of the war) or Chinese-style jian (a long, straight, double-edged sword), while the dadao were primarily used by the rank-and-file troops and police officers - where the dadao gained its reputation as a weapon of execution. The fame of the dadao largely rests on Chinese "big sword" units, which trained with the dadao and charged with them, in particular a charge by the Chinese 29th army - which resulted in a slaughter of many troops (after all, you had soldiers with swords charging Japanese machine guns), but also a few surprising successes. There are some scattered references in Phillip Jowett's China's Wars: Rousing the Dragon 1894-1949, which might be a good place to start looking for additional detail on the combat use of the weapon.

As for the qualities of the dadao itself - there's not a lot of academic information that I can find. u/MartinGreyWolf linked to what is probably the most accessible article on the web. The dadao itself was essentially a long-handled cleaver, and standardization of design seems to have been nonexistent on any kind of a large scale, no doubt due to the nature of China's civil war occurring at the same time as the Japanese invasion and occupation, and most examples I've seen seem to have been made by local blacksmiths out of whatever iron or steel was available.

So when you compare a gunto and a dadao, you have to keep in mind you're looking at traditional-style weapons that were being made during wartime. They were about the same length (the article above says the "ideal" dadao was 35", I've measured my own kyu gunto as 36" from tip to pommel), and both were single-edged weapons, two-handed weapons intended primarily for slashing or cutting attacks - the main difference being that the broad-bladed dadao was designed more for chopping, while the gunto follows the katana in being intended primarily for slicing. The shin gunto was probably made from better steel and to a higher degree of manufacture, but was primarily used as a sidearm, while the dadao might well have been the main weapon of a Chinese guerrilla or "Big Sword" unit, and thus would have seen more practical use.

Quick pedantic note: a Japanese sword wielded by an officer is really a gunto, not a katana. This is relevant to your question because the quality of gunto varied wildly. They could be Sengoku-era blades, or they could be machine-milled 1945 blades. As with all implements of war, quality goes down when casualties rise.

There's a pretty well-researched article about this topic here: https://chinesemartialstudies.com/2013/12/15/through-a-lens-darkly-19-chinas-other-swords-during-world-war-ii/