Cellulose is one of the heavier insulations. However, unless there are serious structural proplems, it shouldn't be a concern. Standard construction (2'OC trusses w/ 5/8" drywall)will allow R-50+ (I personally have about R-65/70. What did you expect! I'm am insulator!).
As far as a lower R-value, your information is mistaken. Standard fiberglass batting has an R of abour 3.2 per inch. Blown fiberglass has an R of about 2.2 to 2.5 per inch. Cellulose has an R of about 3.65 per inch (Even in dense-pack, cellulose maintains an R of 3.55 per inch)! High density batting (such as R-21 / 5 1/2" Fiberglass) in up around that level, but it's quite costly and now your dealing with a heavy batt. Icynene foam has a higher R of about R 4 per inch, but that costs a lot more than even the high density fiberglass.