FFXIV does fairly well telegraphing info compared to other MMOs, but I do think we can improve that further.
For example abilities that can't be dodges (but the markers are there for your info) are a different color / visual style. This allows you to know that you could NOT have dodged it at the point of seeing it, stop trying that- this skill requires anticipation.. or lore interpretation it requires you to utilize your echo. They have markers for most concepts (like "thats going to do alotta damage"), just some bosses don't have them (due to when they were made) - assign someone to make those consistent (allow us to help by allowing a report missing telegraph UI).
Some other textures / effects might be interesting. Like one that indicates a sequence / series of actions (not talking #s like the boss target dash mechanics, just means that 'this ground marker has more to it than just this, like eruption on ifrit'), or the speed at which they will occur.
I might suggest that, if they've done it via a way that can use this, the functions for bosses automatically develop this info. "damage player(2, 3, 4, 10, skill effect), etc etc" and the other UI related functions just sees "triggers 8 effects within 2 seconds" means give it a fast animation speed, undodge-able coloring, with a sequence texture. The point of mentioning that, is because I think when content is first new, particularly, hardcore focused content... don't give all that info (also don't put it into machine memory, only server side). This way those players, who like that fresh learning experience, will get it, and once the guides are being made the game just follows suit. If you don't want the info after that, just remove your echo buff.
I am not sure how exactly I'd like to categorize content types, but I am unsatisfied with just one words (casual, mid, hard). I would probably mix in required player, skill requirement and #, and then increments of expected substantive progress.
So for example 8 party group, 4 veteran, 1 hour. Using this as a goal of design but also a metric to look at if I missed the mark. This tells me I want 8 players, 4 of which need to be veteran, and on average players will experience substantive dopamine hits every hour. So like ultimate might be 8, 8 masters, 12-36 hours. My personal preference is probably set at dynamic scaling of 1 to X, 1 to 1/3 * X, veteran, 15 minutes to 1 hour. Where typically the content is either or "also" scaling to size of group, and only 1/3 really have to know whats up (playing 'well', but no memorization required).