You want to run a game in a universe that already has plenty of heroes, but you want the characters to be in the spotlight and not the heroes that are already a part of the universe. There are many cases when you might run into this. I have run Sailor Moon and Forgotten Realms campaigns, so I know that it is an issue. How do you keep your players from running into overused characters that are an innate part of a universe?
I find that there are several ways around this. You can change the timeline, make it an alternate universe where certain events/heroes never happened, and you can move the characters to a place that the heroes never appear. There are all reasonable ways to keep your games from having well-known NPCs that seem to be in every game in that world.
Changing the timeline can be interesting. It gives the players a chance to affect the things that the major NPCs might do without directly meeting them. The players could complete a mission that the NPCs are supposed to complete which would change what the NPCs are doing during that time period. Perhaps, the players could become the major heroes of the world instead of the NPCs. This is different from an alternate universe because the players are actively changing the universe. In an alternate universe you have already decided what will happen and won't happen. Just remember to take notes of what the group changes.
By making the players be in an alternate universe you have huge openings for campaign ideas. Effectively, you are rewriting the history of that universe and just using the maps, creatures, and other details to your advantage. If you do this, then I would recommend keeping a log of the things that you have changed for your game. It can get confusing if the players run into an event/NPC that isn't supposed to be there.
Moving the characters to a place that nothing of importance occurred is a good option, also. This gives you a chance to explore areas of a world that you might not otherwise explore. Yet, this also allows the main NPCs to make appearances if you need them in your game. There are always small towns and areas that heroes only make guest appearances in. Then, it is also unlikely that the players and the heroes are traveling the same path at the same time, unless you want them to cross paths. So, this is a good way to keep the timeline intact and let your players have the freedom to play without too many major NPCs.
So, don't be intimidated by a world that already has its heroes. You can always make your game new and interesting without worrying about how it will affect the characters. You don't have to include NPCs, which seem a major part in the books belonging to a particular world, and you don't have to include the players in the major events that take place in a world. In any setting there is room to let your imagination loose without worrying about how your players are going to affect that world.