No the exceptions I am talking about are spells with a casting time as an Action.
For example, a Fighter can use the Attack action, not a magic action, to cast Hold Person (a spell with a casting time of an action), a Glamour Bard can cast Command (a spell with a casting time of an action) with a bonus action and not a Magic action, a Valor Bard can cast Truestrike (a specasll with a casting time of an action) with the attack action not a Magic action, A Wizard can cast Greater Invisibility as part of a casting of Contingency without using a Magic action, a Sorcerer can cast Fireball (a spell with a casting time of an action) with a Bonus action and not a Magic action using Quicken spell.
These are all examples of ways that spells that have a casting time of an action but can be cast using something other than a Magic action. These are all exceptions to how "most" such spells are cast. Ready a spell is just one more way of doing this.