Yes many are "just ARM" but due to custom extensions/chips and (in some cases) lack of standard ARM features that doesn't mean they are the same ARM.
This is a stretch at best.
Linux running on M1, Graviton2 (and, soon, Graviton3), Raspberry Pi 3/4 runs same, aarch64 compiled, user space binaries. NetBSD running on M1 and on Raspeberry Pi 3/4 runs same, aarch64 compiled, user space binaries. ARM, the company, enforces the µ-architecture compatibility through the licensing. Just like Intel and AMD do.
The difference is perceptable at the hardware/kernel level; however the same is also true for nearly every new generation of Intel and AMD CPU's – at least some modifications are required in the kernel.
You are conflating software compatibility with hardware availability.
Most ARM vendors sell the equvialent of an electric bicycle when what you need is a van and there are only two viable manufacturers of vans but the first one doesn't sell to companies and the second one requires you rent the van.
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This is a stretch at best.
Linux running on M1, Graviton2 (and, soon, Graviton3), Raspberry Pi 3/4 runs same, aarch64 compiled, user space binaries. NetBSD running on M1 and on Raspeberry Pi 3/4 runs same, aarch64 compiled, user space binaries. ARM, the company, enforces the µ-architecture compatibility through the licensing. Just like Intel and AMD do.
The difference is perceptable at the hardware/kernel level; however the same is also true for nearly every new generation of Intel and AMD CPU's – at least some modifications are required in the kernel.
You are conflating software compatibility with hardware availability.
Most ARM vendors sell the equvialent of an electric bicycle when what you need is a van and there are only two viable manufacturers of vans but the first one doesn't sell to companies and the second one requires you rent the van.