I have to say that I think it’s a big mistake to not require juniors to use 2 entries. This is why we have a drought of top vaulters at senior level- because learning a second vault is very low priority.
It would be better to have them doing a very low value 2nd vault, because at least they would be training the basics of the entry and gives them a foundation to build their 2nd vault difficulty for senior level.
It is no coincidence that vault difficulty and variety progressed greatly during the quad where the most emphasis was placed on different entries. Amanar, Khorkina, Produnova, Zamo, McIntosh, Atler were all pushing the difficulty and innovation at the same time