No, the implication is that raising such a high level of VC would put huge pressure on Substack to grow and enshittify, thereby ruining the platform for writers

No, the implication is that raising such a high level of VC would put huge pressure on Substack to grow and enshittify, thereby ruining the platform for writers who currently think it's good. In other words, their current business model does not support their valuation, which necessitates a pivot.