Also, just two wins at that level means a lot of people are "legends" that you mightn't otherwise consider.
For example, there are many people whose names are often omitted when we go through the big guns of cycling history, especially given that the big GT champions tend to be more well-known the further back into cycling history you go so unless they win multiple times, people who win a couple of the biggest one-day races are lost to time especially if they don't have anything specific that marks their legend (Simpson's and Monséré's premature deaths, for example). The less controlled nature of one-day racing perhaps figures into that, with the number of surprise winners of one day races massively outnumbering the number of true shock winners in the Grand Tours):
Georges Claes (2x Roubaix)
Prosper Depredomme (2x LBL)
Germain Derycke (you could argue that Derycke deserves a lot more credit in cycling history than he gets, having won San Remo, Roubaix, de Ronde and Liège as well as two World Championships podiums)
Noël Foré (1x Ronde, 1x Roubaix)
Emile Daems (1x Sanremo, 1x Roubaix, 1x Lombardia)
Jo de Roo (2x Lombardia, 1x Ronde)
Joseph Bruyère (2x Liège)
That's just restricting it to post-war, otherwise there are numerous people from the early days of cycling that have won a couple of the big races before the sport as it is today was truly established. All won two or more BIG races by your definition (I'm not going to go into the minefield that is the amateur scene in the split Europe days, as Täve Schur should be considered too if you allow for that with 2x World RR, even if he was never allowed to turn pro and attempt any of the other races mentioned apart from the Olympic RR, although anybody who knows anything about Eastern Bloc cycling knows Täve is most definitely a legend anyway).
The more recent you go, the more well-remembered people are, but do we really think that some of the people who only have two such wins in their career will be remembered in 30-40 years as legends, or will they be respected and revered by those 'in the know' and largely lost to casual fans like the names above? Will people really remember Alessandro Ballan, Stijn Devolder, Simon Gerrans or Dan Martin as legends based on their palmarès at time of writing?