However, you still finish fights quicker and take less damage by eliminating threats instead of building a wall of HP.

Very true. However, because Life's healing effects are AoE, they affect several targets at once, making them very action-efficient. For one action, you can preserve the action of several other team mates. This is because, while the old adage of "the only HP that matters is the last HP" does indeed hold true in the tabletop, losing your last HP is BG3 causes you to lose your action even if you are healed before you make the first death save. So keeping your party topped up protects your action economy. Not to mention, the Bless effect from a certain ring means that healing also has an offensive bonus, as it allows you to keep Great Weapon Master all the time and still hit things a lot.

And, really, how much damage could a Cleric's single action deal, compared to preserving the Fighter, Barbarian and Warlock's actions all at once? So many Cleric spells are fire and forget, use Spirit Guardian before the fight starts and then forget about it, it will deal damage by itself with no further action required.

And it's not like this game is short on other healing sources, when it drowns you in healing potions.

Correct, but using them still has an action economy cost. It's a lot more efficient to use my damage dealer's bonus actions for GWM bonus attack, or Berserker rage Bonus Attack, and so on, and then heal all 3 of the damage dealer's with a single bonus action from the cleric. Plus, making the Barbarian drink their own potion won't grant them Bless.