But is omission lying by common industry sense?

You have batteries that decay and processors that scale; It's a feature of the processor that it scales down to protect the battery. If they were the only one in the industry that did it, or it didn't make longevity and safety sense, then maybe not mentioning "we prevent your device from randomly dying or catching on fire as much as the next device" is normal.

I don't see many devices using lipo that sell the feature "we prevent your device from catching on fire by killing it"; though they hopefully all have thermal shutoffs.

I'm not arguing semantics. I'm arguing that they weren't lying. They never stated that they weren't lowering the clock speed when the batteries started to degrade. This may be poor communication on their part but it's not like they ever denied that they were actively doing something to prevent phones from shutting off when they couldn't maintain the power levels needed. Nearly every other manufacturer also does this and those that don't suffer from batteries that shut off randomly or catch fire. It's an issue that's just a physical limitation of battery technology right now.

The word "lying" to me (whether by omission or not) insinuates that the intent was malicious and used to cover up or misstate something with the purpose of misleading consumers. That's not what happened here. The intent wasn't malicious but, rather, to extend the lifetime of batteries that, because of the laws of thermodynamics and physics, were getting to the point where they couldn't sustain performance. They absolutely should have communicated somehow that this was the reason they were doing this but they never denied that this is what was happening because it was assumed that this was common knowledge for LiPo batteries.

I’m not disagreeing one could argue “lying by omission”, but

> they did this by slowing the phones below the specs they advertised

What specs are you referring to here? Apple doesn’t publish processor speed “specs”.