Neonchameleon
Legend
OK. Let's test this statement.By coming at third level it is already a downgrade. You get access to a new spell list at the same time that you get a new spell level and can choose two new at most instead of at the time you choose the most spells known and your cantrips.
Under existing 5e rules a third level sorcerer knows four spells, total. A Divine Soul sorcerer will know a fifth. They can make any or all of these into divine spells.
Under One D&D rules a third level sorcerer knows six spells, having gained two not one at each of second and third levels. The Magical Initiate feat gives them a seventh. Even if we assume the new version of Celestial doesn't give them an eighth at third level they can know one (Magical Initiate) plus two (levelling up to third) plus one (Retraining) divine spells for a total of four - versus the "classic" version's five total. So a third level classic divine soul can have more divine spells than a One D&D Divine soul if and only if they spend all their spell slots on divine magic. This of course makes them almost strictly inferior to a cleric as the cleric has more spells prepared, can switch them up more often, has more hit points, better armour, channel divinity, and their own subclass abilities.
So to sum up a level one OneD&D sorcerer looking at Divine Soul is a strictly better healer than a level 1 classic Divine Soul Sorcerer as they have an extra spell slot. They are also a better Divine Soul Sorcerer at level 3 with access to as many divine spells as a classic Divine Soul Sorcerer who hasn't left their sorcerous casting behind entirely to be an inferior cleric plus two more arcane spells.