Sorcerers Apprentice
Hero
So... an orc? An orc will die in one hit to a rogue's sneak attack, or someone with a greatsword, if you're using feats and they have power attack. Otherwise, the average 15hp on a typical orc will usually protect it from the 2d8+5 damage on the paladin's improved smite longsword. A striker-type character, at high levels, can almost always one shot an orc.
And if you want to drop a dozen ogres with a spell, then that spell had better be Meteor Swarm, because anything less than that (say, a Fireball cast in a level 8 slot) will still average less than 59 damage.
A high-level character can usually one-shot a CR 1/2 orc without spending any resources. A high-level spellcaster can almost one-shot any number of CR 2 ogres by expending a valuable resource.
The problem With using hordes of low Level monsters against high Level characters is that they die too easily to area effects. One Fireball and almost all the orcs are gone, no more horde to fight. Sure the wizard gets to feel really cool but if you want a horde to Challenge the entire party you pretty much have to use bag-of-hp monsters like ogres. After the ogres have been softened up by a Fireball they can be taken out by one or two melee hits.
4E minions may have had only one HP but they also had good defences and immunity to damage on a miss so you could expect to have a decent number left after the horde is hit by a Fireball. In 5E you would need to use ridiculous numbers of orcs to have an interesting figth at high Levels.