It’s true for any variation of Linux. Hell, the vulnerability (Mimikatz) that was crucial in the most expensive cyber security attack in history is still there in Windows.
And for X11 to be exploited you would need to get and run malicious code in the first place. The Linux security model kicks in before you get to that point.
If you can’t replace all of the parts with some other off the shelf part, regardless of quality, then you’re locked to a brand and are at their mercy.
What happens when they inevitably discontinue the A1M and no longer sell parts for it?