Hello Antonio, it seems to me that, from a technical standpoint, even in the 1vs1 globalisation is evident among the various schools, in the sense that, while until 20 years ago you could perceive differences quite clearly, now it's all much more even.
Despite this, in general, players belonging to the best European schools (which certainly at present are the Spanish and the Serbian, at individual technique level), have a better quality of fundamentals: for example, a greater use of both hands, an ability to read the game certainly more advanced than in the young Americans of the same age, although in most cases probably they have on their side a much greater physical potential.
In the case of the Russians, their level of individual technique with regard to shooting is definitely the best of all schools: by frequency of execution and by number of roles on the court which are able to shoot well (in fact in Russia everyone can shoot, from guards to centers); vice versa, with regard to passing, playing without the ball and reading the game, I think probably they are the less developed, as in recent years these aspects of the game have evolved a lot.
All the best, Sergio