I remember that Brewster's fights with the WBO belt already drew large audiences in France, Europe and in USA.
Sure. Wlad's WBO reign also drew large audiences and was even showed on HBO between 2000 and 2003, but it still wasn't a major belt.
You’re being pedantic. There is no specific moment in boxing history when the WBO belt became major. It was a transition, mattering for Hamed and Calzaghe early on and everyone else later on. It sure as sht mattered for Liakovich because Brewster had beaten Wlad and made title defenses in front of big crowds in action fights, and Sergei beat him in a fight where Brewster put in a great effort. This isn’t the same as Hide beating Michael Bentt in the mid 90s and we both know it.