Proposed blocks that fail consensus are recorded and impact the rewards that node providers are entitled to. Usually this is related to performance/networking issues as far as I gather.
Failed block rates are reported in the dashboard I linked to. This sort of stuff is actively being worked on and improved as far as I understand. I also think this falls under the trustworthy node metrics (but I could be mistaken).
Note that if over 1/3 of nodes (38% for a 13 node subnet) are dishonest they could stall a subnet, but that certainly would get noticed. You’d need over 2/3 to have control over consenus.
Certainly still a concern if we have SYBILing NPs