quality of Roman armor than the armor of knights of the XII-XIV centuries

When I was studying the metallurgy of ancient Rome, I saw a rather controversial study done by Michael Fulford, David Sim and Alistair Doig called "The production of Roman ferrous armour:a metallographic survey of material from Britain,Denmark and Germany, and its implications".Here is what it says about the quality of the armor of ancient Rome:

In the material itself there is perhaps a greater variation, from martensitic steel to pure ferrite, but the hardness is consistently greater than about 180Hv. Of our samples, 80% are of ferrite, most showing equi-axed grains from hot-working, and with hardness ranging from 124 to 325HV; the latter (no. 20, Vindolanda helmet) was achieved by heavy cold-working and showed elongated ferrite grains.In all, 64 measurements of different sheets of ferrite give an average hardness of 195Hv and a median of 190Hv. Given that annealed iron is normally 90-100Hv, the extent of cold-working to achieve hardnesses in excess of 180Hv can be well appreciated. Although the samples are small, none of the iron helmets was softer than 210Hv, and none of the shield-bosses was harder than 210Hv. Except for the 3 quenched-steel chain-mails (see below),hardnesses of chain-mail and lorica were between 125Hv and 275Hv(one steel lorica registered 295Hv).

But on the other hand, the hardness of armor in different centuries of the Middle Ages will be as follows (according to data from Alan Williams' book "The knight and the blast furnance"):

Here are some examples: 

By the way, on page 16 of "The Sword and the Crucible", Alan Williams describes Roman metallurgy as "fairly mediocre" in quality.There is another feature, which is that increasing the carbon content increases the hardness of the steel, which seems to be good. However, there is another important parameter - impact strength or the ability of a material to absorb mechanical energy released at high speed. The problem is that by increasing the carbon content, we increase the hardness of the steel, reducing the impact strength and vice versa.

A pure iron Roman plate hardened to 240 Hv will have an impact strength 3 to 4 times that of a medium carbon steel breastplate of the same hardness. By this I want to say that the Roman armor, in theory, should have been even stronger than the medieval one.