Wel I think this exposes one of the design difrences between the editions.
in 5th edition increasing the number of enemies is a way to make encounters harder and is easye to do becouse you might have a bigger number of creatures theye are simple to run.
in 4th the number of enemies diden't increase as much but each enemy became more complex and harder to kill ( more Hp)
Kinda.
In 4e there was a steady progress of bonuses, so monsters needed variants to be used at higher level. But they could have been the same monster with increased bonuses, hp, and defences. Each higher level variant didn't need new attacks or powers. There are 93 variants of orcs in 4e, ranging in level from 1 to 27
We didn't need an orc freak, and orc scout, orc raider, orc harrier, and orc reaver all with completely different attacks. There could have just been a level 1 orc raider, a level 2 orc raider, etc.
Inversely, you don't want the capstone fight to be a series of repeating auto-attacks, either.
True. But capstone fights tend to be unique. They're not something you pull right out of the book. They shouldn't be a textbook encounter.
They're also not the baseline. Generic orcs shouldn't be designed to serve as bosses or unique NPCs.
The thing is that it's always less work to dumb something down than it is to increase its difficulty/options. Even in 4th edition if you wanted the most basic use of a monster you could just have it make basic attacks.
True. My design philosophy does tend to be "it's easier to take away than to add".
But, two thoughts.
One, that's still a decision. It adds a decision point to running the monsters: do I use X or Y. Do I keep all its powers or play it simple. And it adds a trap into the game. New DMs might not realise they can drop powers.
Two, the range of levels where most humanoids are fought singularly is exceedingly small. You start off fighting goblins and kobolds in mobs. After after level 3 or 4 you'll likely be fighting mobs of hobgoblins, orcs, and gnolls. You'd be designing more potent humanoids for a single level.
My party is only 5th level, but in my last session, they raided a gnoll warband to free the slaves kept there. I used pretty much every gnoll statblock I had access to (flind, witherling, hunter, havoc runner, fang of Yeenoghu, etc). Over a dozen gnolls.
I'm super happy for most I could just spam their basic attack. Because when running a dozen monsters, as a DM I need to be quick. And, to the players, it didn't matter and the fight was still threatening because there was a lot of constant danger.
Additionally, even many of the tougher/more singular monsters are relegated to either slapping spellcasting ability on it ('cause that never gets old, right?), or having it be a passive ability such as a medusa/basilisk stone gaze or the rakshasa's cursed claws. The number of creatures with a genuinely unique active abilities is annoyingly small. Even other kinds of passive abilities, like auras, are strangely absent.
Tougher solo monsters get spellcasting because that's what they got in previous editions. 5e is a game inspired by the past, so monsters are designed to work as they they did in the past, to use their classic design. They're meant to be iconic in that respect. So by that design, there's seldom going to be more spellcastery monsters than non-spellcastery monsters.
Funky new powers weren't added to them just because they could.
(If you want monsters with more active powers try new monsters. Such as Kobold Press'
Tome of Beasts.)
Passive vs active...
It's neat to have active triggering powers for the DM. However, those tend to do less damage in order to balance between the funky secondary effects. However, this makes the powers less scary to players. Because the best status effect to place on a creature is "dead". And from the perspective of the adventuring day, unless the ability weakens the character for several combats, it's not going to last long enough to be memorable. Hit point damage will weaken the character in future fights, creating tension.
I've run a few bosses that can buff as an action. But I've seldom used it because the boss only really gets one or two actions, and using one for a buff to allies - half of which will be dead before they get to use it - seems like a waste. It's an option not worth using.
Plus, as the DM, you're narrating the battle, adjudicating the player's actions, running 1-6 monsters, and tracking other events. You have a lot on your plate without adding decision points and active powers to monsters to also pick between and track. As the DM, your number one job is keep the combat moving: even though you're doing twice as much as any other player at the table, your turns *need* to be faster.
Oh, and there is also DM fiat. Players can do whatever you want to let them attempt with their heroes. As a DM it's even easier, as you don't even need to ask. If you want a monster to do something cool... let it do something cool. The player's won't know it wasn't in the statblock. As long as you're being fair and entertaining it's fine.
One of the things the 4e modules did well is have unique room elements to fights. It wasn't just an empty room, but there was blocking and difficult terrain and certain powers were more effective. Or you had to do something else, like closing a portal, disarming traps, or performing a skill challenge.
That's what makes interesting fights.
Rule one of storytelling is "show don't tell". But rule one of DM storytelling is "involve don't show". And funky monster powers are the definition of showing, since it's something another creature is doing. To players, interesting monsters are inherently less interesting than interesting room elements because anything they interact with is inherently more engaging, because it's involving them and their actions/choices.
