To a degree, this is the core of the difference between Conjure animals (2014), conjure animals (2024) and summon animals. 2014 created a pool of Monster Manual accurate creatures to use, each with their own HP and actions. The 2024 version created a collection of spirits that were non-interactable and did a specific effect. The summon spell create one powerful creature that acts like an ally.
The first issue is one of numbers. A horde of MM skeletons are the most versatile out of combat, doing anything from trap detector to caddie to archery. But they create hell on the action economy and are individually too weak (an army of skeletons are one AOE effect away from wasting countless spell levels for animate dead). But for most, this is what summoning minions should be: real actual minions capable of many things that a creature can do.
2024 conjure spells are abstract. They essentially aren't even creatures, they are spell effect zones flavored to describe non-interactable spirits vaguely shaped like the creature type in the name. All they do is is their one spell effect. It's the simplest method of creating a horde (a massive spell aoe doing necrotic damage and causing fear/paralysis/etc) but the least satisfying from a summon standpoint. It's not that much different from any other AOE effect, fluff notwithstanding.
The summon spells create one creature that usually is on par with the level of the summoner (and thus isn't canon fodder) and can be interacted with (has AC and HP) but one summoned creature does not an army make. And your still not really summoning a MM bear, zombie or mind flayer, you are summoning a spirit (again) that can look like those things but has it's own semi-customizable list of options. The best mechanical interpretation, but My Pet Zombie isn't what everyone wants.
Can those different types of summoning be squared? Should it? 2024 Conjure spells and the Summon spells are both in the 24 PHB, and Animate Dead/Create Undead still work like the 2014 type of summon. (More than can be said for pixie summoning druids). But none of those options really brings the fantasy of controlling hordes of the dead. And I don't think you can unless you are willing to give up either versatility or power. In short, I don't think the horde necromancer is possible.