IDK about the specific example of throwing the PCs in water or another plane--that's not usually what I was referring to when I mentioned just throwing scenarios at players.
As an example, I've grabbing one spell list arbitrarily (that first one in your quote) and gone through the latest encounters our group handled to see what they could do off the cuff.
- Clear a 2-floor building filled with monsters that have one-shot potential but are scared of light, the stairs between floors is a chokepoint: A celestial can be used to safely scout either floor. Multiple sources of radiant damage allow them to hit super effectively. With good scouting, death ward saves a fragile character with revivify saves someone if there's a big mistake.
- Survive an ambush in a magically sealed room full of heavy smoke and cover; multiple high-power enemies can apply mental conditions: At-will saves allow them to contribute damage without the hit penalty, wall of fire ignores sightlines completely and you can just guess. Greater restoration can save an MVP if they're charmed / frightened.. Someone is probably going to do, so revifify can bring them back.
- Get an artifact from a small tomb full of mephits and regenerating skeletons. A rival party shows up later to steal it: Turn/Destroy Undead is a freebie, reliable AOE allows them to take on multiple mooks, a summoned celestial or wall can block a chokepoint in a hallway. Banishment as an emergency tool against mephits. Getting someone to drop the artifact if it's stolen with command (drop) gives great post-dungeon insurance.
- Save a town from a dozen mooks with death throes and a fast melee boss in an open town square: Decent ranged attacks let them kite out the exploders, healing word & revifify brings up an ally if they sacrifice themselves to get in a good hit, blindness/deafness is a high-value debuff on the boss. Wall of fire puts something between townsfolk & mooks.
- Rescue someone from an invisible death knight with spell-enchanted armor and his unintelligent stone defenders in a looping dungeon complex: Saves and indiscriminate AOE like sunbeam will let you get full damage if you vaguely know the knight's location, dispel magic breaks his defenses, guidance can pump a stealthy person's check if they want to do solo recon.
All of this would be with regular contributions in combat from their cantrips and
spiritual weapon, with small stuff like exploring without torches thanks to
light, without considering what they could do if they had just a day to prepare (see the user's point on
water walking), and without even considering the free-form options they have from innately-flexible tools like
fabricate and
creation.
And this isn't even particularly crazy. The cleric list doesn't have teleportation, stealth, I don't think it has detect thoughts, locking/unlocking, size alteration. It doesn't have a wizard's access to other flexible spells like fly, counterspell, haste. There's no on-demand defense like shield or absorb elements. Even this middlingly-flexible list designed for primarily PvP unlocks a such a massive breadth of approaches that I could hand them anything I've run since 2020 onwards and they could easily have contributed more than the martial half of the party. Most of my effort would be put towards making them
weaker, probably by giving enemies radiant resistance, inflicting conditions that can't be restored, and threatening to separate them from their allies so they can't easily raise them.