Firstly, I don't want to indicate who is more consistent than Inori in this Junior field (but I think Dalia is a good choice) because until now, the author doesn't introduce many skaters of Japan in Junior field. I'd like to say: the priorities that Japan Team is having right now in international competitions(in this story), is the evidence that Japan has other skaters with good consistency than Inori. The priorities here are:
1. Japan has priority to have 2 entries in seven events: this is the highest priority for a country to get when entering grand prix series (you can see both Inori and Iruka compete in one event, this is 2 entries). To get that priority, Japan team has to have many skaters get medals, or finish at high standings in Junior field for many years. This kind of skaters in Japan can't disapear suddently or all of them go up to Senior field when Inori goes up to Junior field, isn't it?
2. The number of entry that Japan can get when entering Junior Worlds: the author doesn't say that how many slots of Japan is having right now, so your assumption to have 3 slots (and alternatives) into Worlds can't be confirmed. If it's correct that Japan secures 3 slots to Junior Worlds, it means that in Junior Worlds last year, the combined placement of top 2 skaters of Japan team is less than 13 (EX: 1 skater top 1, 1 skater top 8 => combined placement is 9 => secure 3 slots). Thinking that Japan team doesn't have anyone better than Inori is quite unreasonable.
By the way, Inori can be sent to Grand Prix Series (or even Worlds in the future) is the achievement of other older skaters of Japan team. If we don't have them, the only way Inori can compete in those big tournament is getting no.1 at All Japan. This is the current regulation in figure skating.