That is a shailoh for the local posek. The word “local” is important since it would all depend on local conditions. If a community can easily support competition, competition is good. Where it is a problem for the community to support even one kosher grocery store, it might be a problem.
In Boro Park, opening up a frum supermarket is probably never an issue, whereas in a small city it is more likely to be an issue. Similarly, opening up a unique business (consider a supermarket selling only organic foods with good hecksherim) next to its competitor, that is to say another supermarket selling only organic foods with good hecksherim, may be an issue.
Since there are all local factors, you can’t rely on predcedents from other situations and places.