GrapheneOS developers don't make decisions or changes without discussing them first. They weigh pros and cons before doing anything. They're fully aware of the very obvious fact that the boot animation is more visible than the boot key hash. I'm not sure why you're presenting this fact as if nobody could have possibly considered it before you mentioned it.
You're ignoring the very obvious "loading another OS" screen that is displayed immediately before the boot animation and you're assuming that that + a generic AOSP boot animation won't get the same attention as "loading another OS" + GrapheneOS boot animation will.
A project member using the official GrapheneOS account has already said "There's no point in changing this" and they're not going to change something because one person is arguing nonstop in favor of a change. They may very well post more here, but for now I'm locking this discussion because arguing in circles is not productive.