So you maintain that 5 recent monsters (Perytons, Jackalweres, the fellcourt whatever-it's-called and Calastryx), all of which are exceedingly lethal
Jackalweres are from MM3 actually, not from either Monster Vault product. Also that's only four monsters. For things pre-MM3:
Azure Ooze (Dungeon, published around the time that MM1 was around) is absurdly powerful for its level and has a devastating attachment attack. This ensures any PC hitting the character the ooze is attached to takes 1/2 the damage from their attacks. It's also level 7. Plus packed an immense wollop for its time. Now it's just chilling (see what I did there) with most of the newer monsters rather happily.
Storm Shard (MM2) - has a severely punishing "Must move more than 4 squares, or take 3d6+6 lightning damage at-will attack". This is on top of the 1d6+4 (IIRC) damage the power does initially. So that's a level 4 artillery with an at will potential of 4d6+10 damage. Also packs an aura. Combine with allies that immobilize for kittens to be spawned from your PCs all over the table. Incidentally, it's level 4 and if you get knocked unconscious under its effect and the leader can't get to you,
you die! Did I mention it's from Monster Manual 2? I didn't? Well consider that mentioned.
Tiamat who just needs new damage expressions and action recovery so is probably one of the strongest 4E solos. Nothing wrong with her and pound for pound, she can take Calastryx any day.
Any creature that triggers damage off knocking an enemy prone (EG unconscious): For example animated statues (from games day
2008).
Heroslayer Hydra (MM2), who only needs current damage expressions and becomes extremely effective (minding without them is curiously entirely useless, quite the difference!).
Corruption Corpse: Aura 1 -5 to all attacks penalty, explodes on death AND is artillery so reasonable accurate with its pelts of necrotic flesh. Was directly responsible for my first ever TPK along with Otyughs.
I could go on, but the short of it is that you haven't paid much attention to monsters if you think some being very lethal is new
"Nature check + a day off + Enchant Item ritual = New Items (which are possibly better-tailored to the party than the old ones were)" is not my idea of brutal.
Except you can't make rare or uncommon items anymore by the new rarity rules (which I do use). So if your rare sword gets eaten and your DM follows those rules, well that's not a rare sword anymore. Enjoy making your common
Edit: Ghoul (MM), which gain damage considerable bonuses from targeting unconscious characters (Ghoul bite does specifically state unconscious enemies as a target). Killed more than a few PCs with them actually. They were also notable for being ahead of the usual MM damage curve too.
Bloodfire Harpy (MM): Aura 20, 5 fire damage aura. Combine with Beholder Eye of Flame, which has a fire vulnerability aura for hilarious time. Harpies are basically broken in any amount over 2 with the new damage stacking rules (combined with how mobile they are and their other powers).
Dust Devil (MM2): Has an absurd 3d6+3 burst 3 attack and blinds until the end of the creatures next turn. If you recall to the Dark Sun Encounters season, it wasn't a dark sun monster that broke the back of many parties: It was the humble MM2 Dust Devil. Mostly because there were
two of them.
I could carry on if you like. I can actually think of a fair few more creatures pre-MV and even pre-MM3 that are extremely lethal.