For anyone wondering why Regen spells suck compared to actual healing spells, it's because FS doesn't want to encourage passive play. This is why the HP value per FP point decreases with each iteration. The basic regen spell, Replenishment, heals 295HP at 5 HP/sec, which gives 9.83 HP per point of FP. Bountiful Light, the next tier, heals 420HP at 7 HP/sec, which equates to 9.33. And finally, Bountiful Sunlight heals 600HP at 10 HP/sec, which further decreases to 8.57. With each 'upgrade', you consistently get less HP for the total value your FP should net. If it were 1-1 and the upgrade was the HP regen per second, the total heals should be 300/450/700 respectively. Not only that, FS has intentionally rigged Lingering Dragoncrest to extend the regen duration but keep the heal amount the same. Again this is them saying they don't want to encourage passive play. At the very least, you can equip the ring to extend weapon buff from spells and use the extended duration to ensure you get regen, because regen is wasted when your HP is full.
FS has made a point that passives are supplementary in builds. This is why none of the rings are that game-breaking, and you can viably play without them. Instead, FS rewards active actions, such as direct heals. The 4 heal spells restore HP by percentage, and the amount of heal increases with each tier. Assuming 100 spellbuff, you gain 5.6/6.7/7.5/8.5 HP per point of FP, and from there, they scale up the higher your FTH. At 200 spellbuff, all those number double. Projected heal isn't as good, but it definitely has its uses.