In 2008 the Fed was decreasing interest rates, which helped support asset prices. Banks held a lot of bad loans which were worth much less than their balance sheets showed. Both of these factors could have caused the unrealized losses in 2008 to look somewhat small, but the high leverage at banks caused forced asset sales, and the uncertainty around credit losses led to asset prices tanking.

In 2023 the situation isn't necessarily worse, but it is certainly different. Asset prices seem relatively well-understood, in that their declines are a straightforward function of interest rates as opposed to an uncertain function of credit losses. Bank leverage is less than in 2008 as a result of regulation.

If the situation in 2008 was "some banks are _super_ insolvent, and it's hard to tell which ones", in 2023 it seems to be "some banks are mildly insolvent, and it's fairly clear which ones". A mildly insolvent bank can probably stay afloat as long as it continues to have access to capital, which the Fed is giving them. But if people start withdrawing their deposits from one of the mildly insolvent banks, it will become increasingly difficult for that bank to dig out of even a small solvency hole, so there's still some uncertainty as to whether the Fed lifeline is enough to save them.