Let’s look at Trolls.
In 5E trolls are a challenge rating 5 monster. They have 8d10+40 hit points (84 HP on average) and it does not regenerate in any round it takes acid or fire damage. Most wizards are going to have a Firebolt or an Acid Splash cantrip. Trolls are a nuisance, but with their low Dex save and 15 AC they will take damage from a wizard’s cantrip most rounds. A group of trolls can be a problem, but a smart party can focus on one at a time to take them down. With unlimited cantrips a party will almost always have the resources to do so.
In B/X 1d6 trolls could be found as early as the 4th level of the dungeon. A troll had 6d8+3 hit points (30 HP on average) and could regenerate all damage not caused by fire or acid. There were two spells that did fire damage; Fireball and Wall of Fire and none that did acid. Your best bet was using oil which did 1d8 points of damage for two rounds. Hopefully you hit and you had at least three flasks per troll. Neither fireball nor flasks were a great option if you had fighters in melee with a pack of trolls because you probably had a good chance of hitting your own team.
Don’t get me started on “Laser Clerics”, why they need a ranged attack cantrip is beyond me. Why they all need the same one makes even less sense. The Tempest Cleric should at least have a lightning cantrip.
I get 5e is popular and I play it because the DM runs it, but older editions got some things right and Trolls were a lot more trouble.