Well I just hit my first major annoyance with this game - Ranked Matchmaking.
Its probably common knowledge, but I guess the game pairs you up with people who are at similar levels and the same rank.
However, Ive been entering ranked and waiting for the timer to count to zero and kick me back into the lobby for about 15 minutes now. Its irritating.
I dont think Splatoon 1 had this issue, if I remember correctly. It would pair you up woth people at the same rank or close to it, but didnt need the level requirement.
Matchmaking doesn't take level into account. Splatoon 2 has ping based matchmaking so there probably just aren't enough players in your region looking for a match. It's honestly a huge problem since the majority of this game's playerbase is in Japan and therefore won't be matched with most of the world.