I've never played 5E, so a question.... how hard is it to make an NPC based on the PC classes? For example, in 1E/2E it was rather easy to make an NPC fighter of a certain level with certain equipment to face off against the PCs. From what I see of 5E though, character creation is a lot longer process, and NPCs seem to be in the MM with such titles as archmage and bandit....
Yeah starting in 4e, WotC decided making monsters that use the same rules as PC's was a bad idea, so you really can't build a PC sheet and put it up against the players without there being some issues.
Monsters require tons more hit points to deal with players, and generally need upgraded damage. The Gladiator shows this in action; rather than build him as a Fighter, he has some "Fighter-like" abilities (even though a few of them, like Brute and Shield Bash are better than what the Fighter can do), but he's also a CR 5 with 15 Hit Dice (!).
Right. Kind of the point of this is that monsters and PCs are built to do different things.
PCs need to have a variety of abilities which handle different kinds of problems. They need enough stamina to do a whole day's adventuring, but not so many hit points that they're impossible for the antagonists to ever take down in a fight. So usually not a huge pool of HP, but one which can be restored over time with rest, for example.
Monsters need a small range of abilities so they're more manageable for DMs who are juggling several things at once (instead of just one PC), but need enough damage and HP to be useful and scary in the usual 3-5 round duration of a single fight, which is their primary use-case. Giving them the whole range of abilities a PC has is a waste of time and space and puts a huge overhead on the DM.
Classically, pre-3E, D&D never made monsters the equivalent of PCs, but NPC antagonists were the exception. PC stats were a bit simpler in the TSR years, and more standardized, so building a party of evil NPC antagonists was simpler than it would be in the WotC years, but it was still a lot of work to build an NPC party compared with a regular monster encounter, and the stat blocks were much longer.
in 3E WotC made the attempt to rationalize and regularize the whole game, so monsters and PCs almost entirely worked by the same baseline rules. There were a few less-powerful NPC classes, monsters had special Feats, and monster stats gave Equivalent Character Levels, which you'd stack on top of any class levels you gave a monster, but they followed the same basic rules. Every level gave skill points. Every so many levels gave feats and ability bonuses. But this wound up meaning that monster and NPC stat blocks became huge and enormously unwieldy at mid and high levels. It was one of the biggest obstacles to running 3E and 3.5. Putting hours into meticulously getting the stats right for monsters, then them being a giant PITA to use at the table, and most of the abilities and skills going unused in a regular encounter.
Starting in 4E WotC went for ease of use instead, and optimizing monster design and statblocks for use at the table and fun fights. Of course, this has the cost of lesser verisimilitude.
5E rolled back a little more 3E-style. NPC casters, for example, would be given a whole suite of spells like a PC caster. More recent monster books tweaked that more in the direction of 4E, because of the unwieldiness issue again.