Forget IL for dungeon requirements, do this instead.

[Gardes]

An optional solohest training school is enough imo. Call it solo content to learn aspects of multiplay content and give incentives for players to encourage them to do these and try hard to succeed it. Cant be philo or myth tomes for rewards though, you do multiplay content for that.

Imagine something like the guild training hall in monster hunter portables. Those didnt really give you instructions but these should, to hammer in the concepts. Dont kick them out when they fail, just auto reset the instance and let them do it over and over again until the objective of the solohest is completed or they give up.

As a bonus, players can get badges for their training and it can be displayed alongside their name in duty finder. We used to have LS emblems to our name, the ARR mock up had them too. Even if it exists today, it's not really relevant in a random duty finder so the badges can replace that. e.g.: clear various healing solohests, get awarded a..gold 2 star badge, queue in the df as a healer and other players can see that when the dungeon starts.