I don't think doing SCD is ever really a bad career move, because pretty much the most damaging thing you can do to yourself is dance badly - and everyone forgets about that once you've returned to your day job. We only remember the winners and the absolute duffers, and the duffers usually do all right out of their appearance, so no harm no foul
Truth is that even if his schedule were clear, Simon might not have floated the boat of viewers. He just seems to be lacking that spark that makes people engage with what he's doing, for all he's done some routines that weren't bad technically. I've actually found it quite annoying, as I loved his Xmas routine with Katya and thought Kristina would do a great job with him.
Would he find that spark if he weren't so busy? Hard to say - spark's not a quantifiable like technique or 'polish'. There have been instances of people suddenly finding their mojo and being lifted into another marking band entirely. I'll keep my fingers crossed.