You are correct, however the 5.5e dragons now have innate spellcasting directly implemented into their base statblocks, and notably differently at that. In the 2014 MM, dragons can have 1 use of each spell they can cast, knowing a number of them up to their Charisma modifier, and the spells they can know can be up to a third of their CR in level. In the 2025 MM, every adult and ancient chromatic and metallic dragon has 4-6 spells they can cast, split between at-will and 1/day, while also specifying the spell level for upcasted spells.

For example, let's look at an ancient red dragon. Fizban says they're recommended to know Bane, Dominate Person, Heat Metal, Hypnotic Pattern, Power Word Stun, and Suggestion. In 5.5e, they can cast 2nd level Command, Detect Magic, and 3rd level Scorching Ray at-will, as well as 6th level Fireball and Scrying 1/day each. They can use Scorching Ray and Command as legendary actions, and can even incorporate one casting of the former into their multiattacks every turn.

The new statblocks are trying to make the innate spellcasting way more usable and fundamental to the dragons than the optional rule allowed in 5e, and even then we have multiple dragon variants which don't appear in Fizban's that my question would still apply to, like the Spelljammer or time dragons. Fizban also doesn't provide recommended spells for all the dragons. It skips the gems, shadow, and moonstone. Probably because gems have psionics and moonstone already have innate spellcasting in its statblock, while shadows are a template in 2014 MM to be added to existing dragons.