Your advice is applicable to your own original comment, so it seems you do agree with what I said, at least to some degree.
Anyway, in the interests of constructive discussion, let me ask you specifically. Do you think this WEI proposal is good for and why? Does the proposal mention at all what the downsides of this feature might be, or how it could be abused? Is it proposed in such a way that the dominant implementors can't deviate later from the terms suggested in the proposal?
Speed of development. It could take months for a PR to get into Lemmy core and then a new release.
Things that get into Lemmy core have to be well thought out and the core Devs have to want them in there.
Running custom code is a way to make changes without having to get their approval, and if it proves popular enough, then maybe they'll implement it upstream.