Dragons perhaps aren't the best example, as they and Giants are rather notorious as glass cannons in 1e played by RAW. That said, most monster h.p. numbers in 1e are generally pretty low; I found 3e made more sense in this regard though at times got a bit carried away.
Some of the massively high monster hit point numbers I've seen in 4e modules I can't relate to at all; I can only assume 4e adventurers can really bring the pain in big numbers in a hurry.
One thing that has really changed over the editions is the damage a monster can give out vs. the damage it can take. A 1e Hill Giant using a club does 2d8 (I think) damage and has maybe 40 h.p., so a best-case ratio of about 1:2 or 1:3 (16:40). A 3e Hill Giant using a club might do 2d8+8 and have about 100 h.p., giving a best-case ratio of about 1:4 (24:100). A 4e non-minion Hill Giant using a club - well, I don't know what damage it would give out but I'll guess at 2d10+12 - but it'll probably have 200-300 h.p. for a best-case ratio of about 1:8 (32:250)
Don't know the numbers for the hill giant, but I can work it out.
Say the average Hill Giant is a level 12 standard monster (feels about right given ordinary Ogres are level 7-8) and a brute (which is obvious).
Hit points are around level*10+25 = 145
Average Damage for a brute in melee = (12+8) * 1.25 = 25. 2d12 + 12 is about right. Best case ration is just over 1:4, but he probably also has a limited use power for a really hard hit, and some sort of flattening sweep.
We're looking at 1:4
Now the big hit points belong to elites and solos. An obvious elite would be an ettin in the middle of some ogres. Elites have the hit points of two normal monsters of their level, and solos four.
You've been looking at the hit points of Solos I think - so let's take a real one. The
Level 14 Purple Worm. A Solo is not a normal monster - you're expected to generally fight hill giants as a family, but it's the entire party against one dragon. Dragons are the archetypal Solos.
The Purple Worm has 560 hit points. Which seems absurd. Until you realise
one Purple Worm is meant to be more of a challenge to the PCs than five of the hill giants.
Its main attack is "Devour Whole" (it normally uses the Bite for Opportunity Attacks). Devour Whole does 3d10+7 damage (average 22) but if the poor sucker devoured can't escape by the end of the turn it does a further 30 (!) Acid damage.
It then has a minor action attack per round We'll take Fling for 3d10+8 more damage.
(When bloodied it gets a
second minor action attack. Probably the poison sting for a further 2d8 and ongoing 15 damage).
And finally 1/round when you hit the purple worm it Thrashes. Which can do 3d12+5 damage to two separate targets.
So in total, it can do in one round
3d10+7 + 30
plus 3d10 + 8
plus 3d12 + 5 to two separate targets.
It can't, of course thrash at someone it has swallowed at the time. And they won't be taking the 30 damage if they escape.
But using your full damage metric,
The guy it swallowed takes 67 damage
The guy it flung and then thrashed at when he charged back in takes 79 damage
The guy who was just standing too close takes 41 damage.
Both these last two have possibly also been flung into the holes made by the Purple Worm.
Total of 187 damage dished out in the round. That 560 isn't looking so good right now...
And then it has two action points to use in the fight (each meaning it can try to swallow an extra person for the 3d10 +7 (possibly +30) damage) and when it's bloodied it gets an extra action for another 3d10+8 damage.
Yes, 4e monsters with a lot of hit points can generally bring the pain. (At least post Monster Manual 3 - the MM1 Purple Worm is a disgrace).