My understanding is that the steel on the Legacy is 420 whilst the Supreme and Elites are 440, but whether that justifies the price differential is debatable.
What I know, 420 and 440 are steel qualities which are made I guess with "US standards". These steels are used by Paramount skates. Ultima Matrix blades are made in Taiwan and they use AUS8 steel which is made with standard used in Asian countries.
https://en.wikipedia.org/wiki/List_of_blade_materials400 series
The 400 series remains one of the most popular choices for knife makers because it is easy to sharpen and it is resistant to corrosion.
The 400 series is magnetic.
410 is a hardenable, straight-chromium stainless steel which combines superior wear resistance with excellent corrosion resistance.
416 is very similar to 410 with the addition of sulfur to improve machinability.
420 has more carbon than 410, but less than 440. As such, it is softer than 440, but has a higher toughness.[34]
420 series contain several types with various carbon content between 0.15% and 0.40% this steel grade is widely used to make high-end razor blades, surgical scalpels, etc. It obtains about 57 HRC after suitable heat treatment.
420HC (420C) is a higher carbon content 420 stainless steel. The HC stands for "high carbon" and it can be brought to a higher hardness than regular 420 and should not be mistaken for it. Buck Knives, Gerber Knives and Leatherman use 420HC extensively.[11] 420A (420J1) and 420B (420J2) are economical, highly corrosion resistant stainless steel grades. Knife manufacturers use this material in budget knives, also in diving knives due to it's high resistance to corrosion.[11]
440 series has three types: 440A, 440B, and 440C. 440A is a relatively low-cost, highly corrosion-resistant stainless steel. In China, Ahonest ChangJiang Stainless Steel developed 7Cr17MoV, a modified 440A, by adding more vanadium.[35] 440B is almost identical to 440A, but has a higher carbon content range compared to 440A.[35] 440C is also highly corrosion-resistant, but is capable of having a very high hardness. The hardenability of 440C is due to it having the highest carbon content in the 440 group. Because of this, 440C is one of the most common stainless alloys used for knife making.[35] The once ubiquitous American Buck Model 110 Folding Hunter was made of 440C before 1981.[citation needed] Böhler n695 is equivalent to 440C.[citation needed] Knife blades specified as being "440" can typically be assumed to be the lower-hardness 440A grade.
AUS series
The AUS stainless steel series is produced by Aichi Steel Corporation of Japan. They differ from the AISI 4xx series because they have vanadium added to them. Vanadium improves the wear resistance, toughness, and ease of sharpening.[11] In the alloy name the appended 'A' indicates the alloy has been annealed.
AUS-6 (6A) is comparable to 440A with a carbon content close to 0.65%.[11] It is a low cost steel, slightly higher wear resistance compared to 420J.
AUS-8 (8A) is comparable to 440B with a carbon content close to 0.75%.[11] [is often used] instead of 440C.[11] SOG knives uses AUS-8 extensively.
AUS-10 (10A) is comparable to 440C with a carbon content close to 1.10%.[11] It is slightly tougher than 440C