If somehow a user were to be relegated from d4, would that player be demoted to d5 even though all the d4 slots have not been filled. Also does the number next to the division matter? Like is IV 1 more competitive than IV 36? It appears the higher number leagues are more likely to be filled out but I am not sure if its random.
Since IV is the lowest active level in the US, any team that's not under bot control will not demote from IV. The team whose name looks like Connor Quickscopes in your league are an example; if you look at their team history, it shows that they were demoted from your league last year after losing a relegation series but they are still there.