This is the official diagram, which makes a lot more sense:
Ah, I meant for normal people who barely understand the smart home, All your points are probably as valid as can be: I know even less.
The most general takeaway: Matter is not replacing Google Assistant or HomeKit. There is no unification between Amazon and Samsung now. Matter sits below and having Matter support creates a common bridge. Before, clouds had to make bridges one-by-one to other clouds.
Laypeople, like me, hear “application layer” and can misleading think, “oh, application layer = the apps!”, when an app update won’t do anything alone to enable Matter.
The tricky part of the CHIP’s official pyramid (which is not intended for consumers and why should it be) is that it ends at CHIP, but consumers won’t ever interact with CHIP directly, but through another ecosystem/cloud that has CHIP support.