You need a very complex weighing and revocation mechanism because once one bad player is in your web of trust they can become a node along which both other bad players and good players alike can join.

Trust in the real world is not immutable. It is constantly re-evaluated. So the Web of Trust concept should do this as well.

Also, there needs to be some significant consequence to people who are bad actors and, transitively, to people who trust bad actors.

The hardest part isn’t figuring out how to cut off the low quality nodes. It’s how to incentivize people to join a network where the consequences are so high that you really won’t want to violate trust. It can’t simply be a free account that only requires an a verifiable email address. It will have to require a significant investment in verifying real world identity, preventing multiple accounts, reducing account hijackings, etc. those are all expensive and high friction.

Build a tree, cut the tree at the first link, now you get rid of all of them. Will have some collateral damage though, but maybe safe to assume actually "good players" can rejoin at another maybe more stable leaf

Then I can see who added that bad player and cut off everyone who trusted them (or decrease the trust level if the system allows that).