Let's be careful to remember that there are different levels of effort and understanding required for different levels of security and privacy. GrapheneOS has taken the approach of offering harm reduction, with sane defaults and options that allow advanced users to take near-complete control over their device (within the limits of the Pixel hardware). This is obvious by their inclusion of the sandboxed Google Play Store as a major feature of the OS, as it is much better than the situation on Google's Android. It is also not installed by default, forcing users to at least somewhat educate themselves in order to install it.

Accrescent is right in line with this philosophy, and is also not installed by default. Of course if your threat model (or desire) is to achieve the highest level of online anonymity and to have a completely FOSS system, you should not use it... of course you probably shouldn't use FDroid either, in that case, and should build from source. However, you are clearly in a situation where your threat model does not require those lengths, and FDroid is more of a principled choice.

I think its pointlessly inflammatory to call Accrescent "dangerous" just because it allows for non-FOSS software. Now if you want to criticize whether or not it is fulfilling its stated goals, that is another story.