It's quite excessive actually. If I recall correctly, not only is it a Lvl 35 Solo Soldier (with all the defensive craziness that implies), but it also has a power that gives a -5 to attacks.
The thing is that Cthulhu would not be that powerfull in D&D. In 4e he might not even be a solo but only an elite (a treatment that several demigods suffers in 4e).
Cthulhu has the advantage of being from a setting that has only crappy mortals in it. Cthulhu mortals lose sanity upon seeing monsters that merely make a D&D hero yawn.
Cthulhu has not to deal with entities such as Orcus or Pelor in his own setting and even in his own setting Cthulhu is not the biggest fish but pales before the likes of Nyarlathotep & Co.
In 3e Cthulhu received offfical D&D stats and he was a divine rank 5 demigod (Azathoth was a divine rank 20 greater god).
Building from there, a 4e Cthulhu could easily be a level 29 elite while Azathoth would stand as a level 39-40 solo on eyelevel with the likes of Moradin of Tharizdhun).
But a level 29 elite Cthulhu can't eat 1d4 heroes per round? Sure, because these heroes are not mere investigators but are demigods, primordials, archfey, .... in their own right

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.