I will never get the huge sizing discrepancies in clothing, especially footwear. Maybe this has been discussed before, and if so sorry for bringing up the topic again.
I mean, for any shoe sizing system, European, UK, US or whatever, there should be a direct correlation between a given size and the length of the foot in centimeters/inches.
For clothing it can be trickier because for example for tops it's not only the chest, there's also shoulders, arms, length..., same for bottoms, it's not just the waist, also rise, thigh, length, leg opening... also there are also clothes meant to be fitted and others looser, but there's not such a thing for footwear. There are obviously chunkier and slimmer shoes/boots, but that should only have to do with their looks on the outside and not sizing/how your feet fit inside.
And I know that when we talk about artisanal brands which produce goods "fatto a mano" there might be small variations, but if we talk about consistently sizing up 2 for a brand it seems like an easy to fix issue, doesn't it? Especially when this can be detrimental to the brands themselves, which can see their products being returned over an over again to retailers.
Sorry for the rant but this happened to me recently when I bought a pair of 10sei0otto boots... since it's not one of the brands discussed here (which are higher end), I couldn't really find references about how their sizing works, only to find out that they run at least 1 size large. So me, a true 41 had to buy a 40 in 10sei0otto and if I wanted to buy some Guidis I would have to buy a 43, a variation of 3 full sizes, it's ridiculous.