As I was saying...
Club rides I think can help build certain racing skills. Specifically:
4. Economical riding
5. Peleton confidence
4. Economical riding, in one of the cycling books I came across a quite that basically said in a race, if you ever have to apply the brakes, it means you've pedaled too much. That's a very easy thing to work on in a club ride. Partly because on a group ride you want to avoid anything like sudden braking (or other unexpected manoeuvres), so it's just good and safe form to brake as little as possible.
And as well you can start to figure out how to let hills work for you. There is one particular downhill/uphill combo on one of the Flyers' regular rides that I used to pedal furiously down – to get up speed, right? for the hill at the bottom of it. Inevitably I'd get passed by half the pack going back up. Then I figured out that a few turns at the top and getting as aero as possible going down got me almost as much speed but without the effort. And allowed me to hit the hill going up with lots of gear & cadence to work with. Much better, much easier, much faster.
It's also a good place to informally practice echeloning and staying out of the wind.
5. Peleton confidence, in the end really, does require actual racing. I'm not sure if I'll ever really get there. Scares the shit out of me, actually. But as a starter, group rides do allow you to get comfortable riding in close quarters with a lot of people. Building skills like: bike proprioception; knowing what it looks like to be 10 cm back of the wheel ahead of you without looking at your own front wheel; learning to look through and past the rider ahead of you; moving into open spaces; that sort of thing.
You can train up stuff like your endurance, your power and your lactate threshold on your own, but a lot of the soft skills of racing, I think, can only be practised in a well-organized group ride.
And as a bonus, they are a lot more fun than training alone. IMHO.