I don't find these reasons particularly compelling.

"To help clients that don't yet implement reports..."
In what way would this help those clients? They should probably just implement reports rather than just having a warning sign emoji show up as a reaction to a post. And that is assuming they have that array of reaction types available. As mentioned by nostr:npub1jlrs53pkdfjnts29kveljul2sm0actt6n8dxrrzqcersttvcuv3qdjynqn, if they haven't implemented reports, they may also only have one reaction type visible in the client, and users of #Amethyst just have to hope they don't display all kind 7 reactions as a positive reaction on their client.

"...to help content indexers figure out how good a post is..."
While negative reactions, when they are unambiguously negative, can help content indexing, so could reports, and with less ambiguity. I can think of situations when I might react with what could be considered a negative reaction, but not because I don't value the post at all, or wish it hadn't shown up in my feed. For instance, someone might post about how there are parents intentionally mutilating their children because they "feel" like they are a different gender, and the OP is clearly against this. I would probably react with a puke emoji 🤮 IN AGREEMENT with the OP, even though that is a clearly negative reaction. Likewise, if someone posts something alarming about some garbage that is being put into processed food that I had no idea was the case, I might react with ⚠️. That should not reflect on how "good" the post is, as it might be a very good post about the dangers of processed garbage in our food. However, reports should definitely have bearing on how good a post is, and lack of reactions can speak as loudly as reactions.

"...to help clients that do not want to implement reports because they see as too harsh and/or form of censorship."
I am unsure how this helps such clients either. If they don't want to implement reports, then reports just won't show up in their client. Reactions may show up, if they have the ability to display a wide variety of reactions, but anyone using the client won't necessarily know that a ⚠️ reaction means the note was reported on another client, unless the client displays that specific type of reaction as a report, in which case they should just implement kind 1984.

It is my understanding that how "soft" or "hard" a report function is can be determined by each client, right? Each client can choose what a report results in for their client. Maybe one client will blur any images on notes that have been reported by people you follow. Another will do so with anyone in your entire web-of-trust. A more harsh client may choose to hide all posts that have been reported by your web-of-trust by default, and only show them if you turn this feature off in your settings. But ultimately, each client decides how a report affects their users' feeds, so it can be as "soft" as any client prefers it to be, including doing nothing with the information at all, or simply displaying something saying "5 people you follow have reported this note," but showing the note to you anyway.