My personal experience with this is that the ratio matters A LOT. I.e. having juniors out number the seniors is bad.
When you have a team that mostly consist of junior and mid-level developers, then they will clique together and they will mostly likely "behave" like juniors. Typical junior behaviour is e.g. to rather than digging into the backlog for the next thing to work on when you're done with one thing, to just sit around and wait for a senior to give you the next task.
However, if you have a team of seniors, who behave like seniors, adding one junior to this team, the junior will in no-time start to behave like a senior. Act by example. Before you know it you will have a really valuable team member.