EDIT EDIT: And I dunno what that is about enchantment. Enchantment rocks the house. Lots of bruiser monsters and things you can shut down completely with enchantment. The problem is if you go will save focused, and then you're fighting undead for the next 5 levels. Also some DMs fucking hate save or dies and will shut you down if you focus on them by piling on massive saving throws or immunities - this comes under 'bad DMing'. You are the DM, your monsters are SUPPOSED to die. If they die too quick, make more shittier monsters not one big monster and look at that the single target SoD specialist is suddenly using shitty fireballs. Ofc if you then do that 100% of the time, still shitty DMing.
A lot of things are theoretically highly effective, but run up against game restrictions.
Enchantment and Necromancy are extremely effective when they do work(and given the monster array in the MM its safe to say they'd work most of the time given a random spread). They defeat enemies quickly, with SoDs, hard-to-resist(barring immunities) debuffs and convert enemies into persistent minions.
Of these, SoDs are immensely unsatisfactory to GMs, because they either fail or end encounter. So for any encounter they are invested into, the GM WILL impose countermeasures. So, to a lesser degree, when it is really important(boss fights), you can't rely on SoDs because they are going to meet countermeasures, even with good GMs. To a greater degree, a bad GM would just make basically half of everything you meet immune to your specialty.
The harder part is where they get you minions. Sure you could do the same with conjuration to bind outsiders, transmutation to get you exotic abilities, divination to read the plot, necromancy to raise/control undead, enchantment to mind control anything with a mind...but actually running these is a pain.
Minions need to be managed, each minion more complex than auto-attack has to be kept track of, each creatures health and gear...these are things that make you lose the ability even if it wasn't overpowered, just because its annoying to manage.
Divinations could read the plot, but while whatever you contact with the magic might be omniscient, the GM is only omnipotent, and often don't have anything for you to find out in the first place.
These are probably metagame traps. They are traps purely because their metagame difficulties makes it extremely unlikely that they'd work as expected. Or that you want to, by the time you're managing your third mind-slave.