That’s all very fair comment but please, please don’t think about entering a road race or crit until you’ve got a big pile of group rides under your belt. Spartacus doesn’t need to practice riding in a pack.
There are a lot of misconceptions about what “pros” do or don’t do.
No one does everything all the time. Cancellara may have been answering a specific question and the answer may have gotten generalized by the time you heard it.
A good mix of group and solo riding with purpose for every workout is the best way to get the most out of your training. That’s incredibly simple advice that the majority of people cannot pull off.
If you go to a group ride where they are faster, then you will get faster. Also, the bursts of group rides really help out; especially if you are holding onto the back. However they are really dangerous.
Personally though, I don’t care for them. My biggest fear isn’t that I crash, but I crash someone else. I’m a pretty adept cyclist but your skills aren’t the only thing to keep into account. Also, being asthmatic, I’m much better suited for individual TT’s. It goes away if I start easy but if it starts off as a hammerfest and I get an attack I’m done. My last group ride this happened and I had 2 guys babysitting me, which was nice of them, but a position I don’t want to put myself in that position again.