Yeah, but it's got resist all damage 10. Plus it's immune to charm and fear effects. It gets all its saving throws at +5. It has blindsight 20. It has reach three, and it's a 4x4 creature (could be bigger if you wanted).
The resist all should be obvious. Immune to charm and fear? You're not going to be swaying or distracting this guy any time soon. Fear... are star pact warlocks nerfed? Sounds like.
Saving throws at plus five... good luck getting any effect to stick more than the one turn! He laughs at your ongoing damage! Dazed? Stunned? Not for long!
Blindsight 20 means that the tarrasque can see invisible and concealed creatures at a distance of 20 squares. Well, that nerfs the warlock, the rogue, and a significant chunk of the wizard, now doesn't it? Oh, and the drow's magical darkness that blinds creatures? Doesn't matter.
This is a creature that, at a minimum, totally dominates a 10x10 square. It can move, then, as a standard action, move again and trample people for an average of 20 damage. Every third turn, it'll doing 20 damage (ongoing fifteen) and either doing 35 damage and ruining your AC or doing 35 damage and knocking you prone!
The PCs are plinking away at him for 50 damage apiece when they get lucky, meanwhile he's doing 50 damage a turn. It'll take them 15 attacks to bloody it, at which point it'll knock it up a notch and start doing 20 damage, ongoing 15, to everyone it can reach. It'll take another 15 attacks to kill it, and it'll be able to kill a PC in roughly 6 turns.
Rogues can't get CA, warlocks and wizards can't get effects to stick, and fighters are just asking for the privilege of dying first.