Celebrim
Legend
They certainly are and that's part of the problem. There's nothing wrong with them being a powerful melee combatant. But when 3e started giving monsters bonuses to hit based on their stats, the system generated a very powerful melee combatant whose threat level lobbing rocks dropped off significantly compared to his 1e/2e counterparts whose ability to hit in melee or at range was dependent on pretty much just hit dice. The system may work pretty much seamlessly when comparing PCs and NPCs, but it probably makes the giants too nasty up close but not nasty enough at a distance.
If you are really concerned about this, giving giants a larger racial bonus to accuracy when throwing rocks would let them pummel parties from a distance.
Besides which, I'm thinking your referring to the classic case of 1e as you experienced it. In 1e as I experienced it, giants were among the more feared opponents precisely because their ability to hit wasn't just based on HD, but they got bonuses to hit from their strength - making them one of the few foes that could challenge a PC in melee once you got better than 0 AC. Frost giants got +4 to hit and +9 to damage when using weapons in all the 1e games I played.