It isn't true it comes solely from content creators.

Apart from the fact that literally all rewards come from investors who are paying them (via inflation), not from people who receive them, it comes from the reward pool which pays both authors and curators (stakeholders). The latter will absorb either a 25% share or a 50% share of the SPS budget depending on whether you based it on the existing split or the post-HF21 split.

But, again, all rewards are paid by investors. Shifting around who receives them does not change that.