From the standpoint of challenges, the game does lack the content each VU. in 4.3 the challenging content is just the new EX, dungeon is a cakewalk and the other new battle content is tuned to be easy.
In theory the Ultimate content would be released at the same time as all other content but for the sake of allowing players to finish other content before grinding ultimate they hold it off for two weeks.
With Deep Dungeon I'm not certain but I do wish this content could see more production earlier in the patch cycle rather than the 3rd Version update, pretty much a year after Stormblood release, it provides the most bang for your buck when it comes to challenging content on top of RNG to get loot that other content doesn't provide.
Though there is also the question of wasted resources, aka Squadrons, releasing 3 new areas NPCs can go to with players does use up resources that could be used to make other content I honestly don't see the worth of doing Squadron instances since the game already provides a bunch of other ways to level a DOW/DOM. If they had worked it to be it's own entity unique from just npcs can go to dungeon with you and play as well as Tataru plays arcanist. . .
What could help a lot is if SE considered releasing standalone boss encounters of all the raids tuned to 8-man content. Imagine all the bosses but extreme versions, while yes it would require resources to produce it would have the benefit of already having the main assets designed for the boss while adding more layer on top of it.
Basically using what they deemed overtuned fora casual 24-man experience and create unique challenging 8-man encounters.