Clerics aren't required because you can't typically fight the HP drain of combat with healing spells. You can't keep people topped up, so at best, you can stop them from taking saving throws or being finished off if the party is forced to retreat.

There's still good reason to be a cleric. They're heavily armored and punchy with brazenly above par spell damage. Debuff removers are clutch in combat more than hitpoints, and clerics still come with similar utility and versatility you find in a Wizard (plane shift, water walk/breathing, tongues, dispel magics, etc)

Of course, they're wizards that require a federally approved government budget at high levels. 1000gp for pork'n'beans dinner here, 1000gp magic 1-up rock there, 250gp for a plane-swap fork. Even summoning requires an immigration waiver or a really good diplomat.

Clerics just don't add that much to the party besides being the companies' insurance policy and looking shiny and powerful at low levels. When you're up against fireballs and cloudkills and prismatic sprays, trading in HP just doesn't pay out.

Clerics aren't required because you can't typically fight the HP drain of combat with healing spells, even with one, unless your DM's softballing the party. Healing spells definitely can't deal with the party getting hit by high-level AOE's. A 1d4+5 Mass Healing Word won't compete with an 8D6 (28 avg) fireball for hitpoints, even though they are both level 3 spells. Not even a level 3 3d8+5 Cure Wounds spell can (only 18.5 avg).

5e epitomizes the principle of "A good offense, Period." I have trouble looking at a Divine Soul Sorcerer seriously because of this, since they give up some pretty powerful options for a short list of some of the weakest (heals), most financially expensive (revives), and/or circumstantial effects (restorations).