Why do you feel that way? Just the aesthetic? Because I know some models that look WAY worse than the Forsaken
Organic mutation sprouting from a mechanical source is probably difficult to execute properly (i'm not a sculptor so I couldn't say for sure).
If you look at lots of Chaos models being produced by
GW in the last 10 years, they've made a concerted effort to make things look more and more mutated. Some of it looks good (The old
40K Daemon Prince (which is actually more like 15 years old now but clearly sculpted by hand), Death Guard, Dark Vengance for example) and some looks down right terrible (Plastic Daemon Prince, Possessed, Forsaken, Skull Reapers/Wrath Mongers)
You can see a distinct transition in style when
GW started to sculpt things using
CAD. Around 2007, everything started to look very angular and chunky. This is a result of
CAD design and getting used to sculpting with new technology. A lot of the models produced around this era are pretty bad. A lot of the organic mutations on these models looks tacked on, and
IMO absurdly cartoony when it should look genuinely terrifying. Even up until now those Skull Reapers look absolutely terrible. Their mutations look stupid, not scary. A lot of Chaos looks like a saturday morning cartoon show, when it should look like the most terrifying horror film you've ever seen.
It's a fine line, and not a lot of sculptors know how to execute it properly.