Someone with the motivation to install custom firmware would consider the bootsplash aesthetic a deal breaker?

Yes -- bootsplash showing "DANGER! YOUR SECURITY AT RISK! HACKERS CAN NOW STEAL YOUR GIRLFRIEND AND SHUFFLE YOUR PAIRS OF SOCKS!" in big bold red letters only because you enabled root to remove manufacturer malware (which if anything likely _increases_ your security) is a deal breaker, because it will frighten most users from doing it .

If you want to promote alternative bootloaders or OSes for wider, nontechnical audiences (like LineageOS etc), then absolutely.

I think it's a difference in mindset whether you view custom firmware as a grudging exception for techies (with the understanding that "normal" people should have a device under full control of their respective vendor), or whether you want an open OS ecosystem for everyone.