I enjoy learning every day. And -generally- I'd like to know, where my knowledge has limits. You seem to care, and claim to be wise, so please, do enlighten me

I enjoy learning every day. And -generally- I'd like to know, where my knowledge has limits. You seem to care, and claim to be wise, so please, do enlighten me, where I'm wrong. We may be misinterpreting, what the other one is trying to say. I'll try to re-word what I mean: If your "system" uses standard off-the-shelf parts (CPU/SOC/Mem/...), then the fact, that you can go out to the shop, and buy standard replacements, means that you can be reasonably sure to be able to thwart/detect a targeted attack on your supply-chain easier, than if your device contains a e.g. custom, specific CPU for that device, that could contain god knows what extensions to the instruction set, and that you can only get a replacement for from that one specific vendor. Or where do I have dent in my logic?