Spell Versatility is appropriate for the Bard. To swap out one spell per rest (but not all spells) is needed. Magical Secrets remains unavailable until the higher levels, from level 10 and up. But most of the experience and feel of the game is before level 10. Many campaigns fail to even reach the highest levels. Magical Secrets shows that versatility is thematically suitable for the Bard. Not only to gain special access to spells (Magical Secrets), but to make use of spells that are available (Spell Versatility). Some spells are more useful in many situations, while other spells are highly situational. Spell Versatility is necessary to allow the class to make use of those more situational spells, that the designers intended to be available.
I love where the Rules Tip specifies that one cantrip can be swapped.
The Sorcerer needs Spell Versatility for the same reason as the Bard, to make situational Sorcerer spells practicable. But thematically, it might seem less appropriate for the Sorcerer. The concept is the nature of the Sorcerer is inherently magical. So, swapping spells comes across as fundamentally altering ones own nature, like modifying ones own DNA sotospeak. It is awkward. But mechanically, the Sorcerer needs it, or else many Sorcerer spells that are more niche will never see the light of day (or the dark of night). Flavorwise, it takes effort to make sense of Sorcerer Spell Versatility. It is ok for one latent power to emerge while an other inherent power goes dormant. But it takes more thought to explain how this is happening.
I am satisfied with Wizard Cantrip Versatility that allows the Wizard to (officially) swap out one cantrip while leveling. It might surprise that the Wizard can only swap a cantrip while leveling, when the Wizard is simply preparing a spellbook spell, while the Sorcerer whose very nature is inherently the cantrip can swap it at any long rest. For me, the Wizard cantrips are especially important because they mechanically actualize the concept that the Wizard oneself is inherently magical (not the external spellbook). The always-on magic shows the magical potential. The Wizard can eventually learn and master the multiversal forces of magic. But it is the inherent cantrips that evidence the inherent capacity for magic, and the sensitivity to magic. The Wizard too has a magical nature. So, for me, the reason why it is easier for the Sorcerer to swap out a cantrip and more difficult for the Wizard to do so, is because the Sorcerer is more self-aware, more sensitive to ones own magical nature including latent magical potential. By contrast the Wizard is more outwardly oriented and less aware of inner potential.
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