Basically, it's the same with glasses, medallions and Svens. The glass gives +3 on one stat, the medallion +6 (two on each of the 3 needed stats) and a Sven gives +15 (so 3 on 3 traits and 2 on the 3 other traits)
Even though they are not clearly seeable for us as gamers, each horse of course has their traits represented by numbers. The numbers decide if a horse is sub-par or World Class