No, not really. Equity loss is unrealized loss -- it's just on paper because the stock price is down. If Rivian's share price goes back up, that loss becomes a gain.
Whereas the $3B net profit is real money they can put into their coffers (or share with shareholders).
Edit: now if Rivian goes bankrupt and delists, then yes, at that point Amazon does lose however many $Bs they invested which they will put as a write-off.
They invested ~1.3B for an 18% stake in the company. At todays market cap that’s 2.6B for a profit of 1.3B from initial investment, or a 100% gain on their investment
Whereas the $3B net profit is real money they can put into their coffers (or share with shareholders).
Edit: now if Rivian goes bankrupt and delists, then yes, at that point Amazon does lose however many $Bs they invested which they will put as a write-off.