Can a good interview prep course be a substitute for real experience building software?

Nope.

While resources like good courses can help as a good starting point (and it looks like the one linked in the post isn't that good), actually writing the code (and striving to do it well) is what truly gets you there.

I'm living proof of this: I have passed every system design interview I've ever done without really studying.

How did I do it? I just built a ton of Android stuff:

1. I got great experience building Course Hero's Android app from scratch and scaling a core Instagram feature (ads) to billions of users with $5 billion+ in yearly revenue. I pushed hard to make my code great with solid architecture.
2. I have published ~30 Android apps with 4 million+ users. These side projects were extremely helpful to diversify app types I've worked with and better understand the core Android concepts (these are often abstracted away at Big Tech).

If you're more on the front-end like me and that LinkedIn post (iOS), you're also going to get a bunch more practical coding rounds where you need to build a real piece of software from scratch live. You can't study your way out of that one.

If you want to get a top software job at a top company, you need to actually build top software. You can't just study some courses and books, memorize some fancy terms, and sneak your way in. Again, these resources can help, but you need to augment them with real coding, either at your job and/or through side projects.

For resources on passing system design/practical coding interviews organically, I recommend these:

• System Design Masterclass: Taro Playlists
• "How do I learn how to write clean, reusable, and scalable code?"

Hard to deny that building is the best form of learning. However, having a good guide or tutorial can help accelerate learning.

Quality matters a lot.

No. The simplest example from my experiences that tear this down is to attempt coding a fix for a critical outage (bonus points for a heavy regulated industry). Like Harry Potter once said in book 5, there's a huge difference between reading about Defense Against the Dark Arts theory and an angry Lord Voldemort spamming "AVADA KEDAVRA" at you.