Game design ramble incoming.
This is true in theory, in a game design sense. Shielding is mechanically more powerful than direct heals or regens. What is meant by this is, take a straight heal. Keeping all other things the same (resource cost, cast time, targets, range, total potency, etc) and slap a shield on it. That heal is now more powerful than it was before. It's capable of salvaging more situations than it originally was. The opposite is true of a regen. Take a heal, parcel its potency out over time. It's now capable of salvaging fewer scenarios, because, again in a vacuum, its potency alone might get someone killed if it can't outpace the damage.
This is the root of why shielding spells are more resource-expensive than normal heals, and regens are cheaper. It's the price tag for mechanical advantage. Now, these can be priced in a way that makes the regens better outside the spherical cows world of the design vacuum, but it's why shielding is "better".