Oh boy.

Hold Person is incredibly OPed in the gold box games, and its worse because ALL THE CLERICS ALWAYS CAST IT.

To be fair, it was overpowered in 1e too. Even at level 10, it's usually a coin toss if it gets you. And if it gets you, you're screwed.

It really, really, REALLY makes attacking temples a very big pain in the gluteus maximus.

And this being Dungeons and Dragons, temple raids happen a lot. Heretics are enemies just as often as goblins and orcs.

The fact that sleeping or held targets can be killed in a single hit is what I feel pushes these spells over the edge in terms of power.

Non-D&D CRPGs tended not to have that mechanic. In Wizardry, a sleeping target can be hit for extra damage IIRC, but is likely to wake up at the end of the turn. In Dragon Quest, sleeping targets don't get any turns (not sure whether they can still dodge attacks, but I note that generally attacks rarely miss, unlike in D&D), but they still take normal damage from attacks; even still, being put to sleep is still frequently a death sentence, so enemies that can cast Sleep are generally feared. (It's bad enough that, when power leveling (which is required in DQ1), players tend to prefer areas that don't have Sleep casting enemies.)

Honestly, I don't like that instant kill rule, or the Coup de Grace action in later editions. Missing turns is enough of a penalty for failing a save against a sleep effect; having the player be at severe risk of death is too much IMO.

I seem to remember old AD&D's Sleep spell not even allowing a saving throw; if the low level PCs were to encounter a 1st level mage capable of casting the Sleep spell, there's a pretty good chance of a TPK, or at least multiple character deaths, and that's just not right. (If you notice, I'm pretty sure that all the AD&D based games avoid giving enemies that particular spell, which is way too powerful for a 1st level spell.)

In later D&D editions, as well as in Pathfinder, affected targets get a new saving throw each round against sleep and hold effects, which helps mitigate the issues with these spells somewhat, but I still think these effects aren't that fun for a player whose character is hit by one of them.

Wands of Fireball and Necklaces of Missiles are excellent for disrupting enemy clerics' spell casting. Items generally do less damage than spells, but have the benefit of instant casting.