The fact that I can unlock and relock the bootloader is not a security issue or a risk. People who don't know what that means cannot possibly do it by mistake.
Now allowing root access to users on Android, that's a security risk because a user can be tricked into giving root access to some evil app. I don't have root access on my GrapheneOS, even though I chose to install it myself. Because it is more secure like this.
So it sounds like a fair compromise to me: they make Android the way they want, and if I don't like it I can install an alternative OS. Just like I can install Linux if I don't like Windows. What I don't like is that most Android manufacturers actively try to prevent me from doing that, and I don't like it.