I do think you've isolated exactly what made old Zelda combat difficult. Enemy aggression was only a small part of it, enemy variety is a bigger thing. It happens in Monster Hunter as well, where the lesser wyverns can become a big danger when combined with a full-fledged Monster in the room. The insectoid Bnhabra, for instance, have a sting which can cause total paralysis for critical moments if they sneak up on you, or a projectile they can shoot that brings a defense (i think?) debuff. These enemies are such a non-threat by themselves, but add a lot of danger to an already dangerous fight with the monsters.
In Zelda's case, of course, no one enemy is as dangerous as Tetsucabra or any other Monster, but then the lesser enemies are also more aggressive, and there can be more of them.
Monster Hunter: pissing me off since 2010.
