AFAICT, as of commit a0a422c,  we have 2 different logics to evict outbound peers : lagging-chain (`ConsiderEviction`) and (`CheckForStaleTipAndEvictPeers`). The former to sanitize out lazy/buggy peers who have never sent us a valid header and are always staying behind our tip, the latter triggered in case of stale tip due to block variance to seek a better chain by rotating our outbound peers if we already reach an outbound limit (`EvictExtraOutboundPeers`).

Block-relay-only peers were introduced by #15719. Contrary to outbound full-relay peers who provided us at least a useful header, they're not protected by lagging-chain eviction.

We actually have a comment inside `ProcessHeadersMessage` indicating the contrary behavior. We should either document cleanly that block-relay-only aren't protected or effectively extend the scope of protection to them.

Hinted during #19724 review, see https://github.com/bitcoin/bitcoin/pull/19724#discussion_r475144532
{
    if (state->pindexBestKnownBlock && pindex == state->pindexBestKnownBlock->GetAncestor(pindex->nHeight))
        return true;
    if (state->pindexBestHeaderSent && pindex == state->pindexBestHeaderSent->GetAncestor(pindex->nHeight))
        return true;
    return false;
}
/** Update pindexLastCommonBlock and add not-in-flight missing successors to vBlocks, until it has
 *  at most count entries. */
static void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<const CBlockIndex*>& vBlocks, NodeId& nodeStaller, const Consensus::Params& consensusParams) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
{
    if (count == 0)
        return;
    vBlocks.reserve(vBlocks.size() + count);
    CNodeState *state = State(nodeid);
    assert(state != nullptr);
    
    ProcessBlockAvailability(nodeid);
    if (state->pindexBestKnownBlock == nullptr || state->pindexBestKnownBlock->nChainWork < ::ChainActive().Tip()->nChainWork || state->pindexBestKnownBlock->nChainWork < nMinimumChainWork) {
        
        return;
    }
    if (state->pindexLastCommonBlock == nullptr) {
        
        
        state->pindexLastCommonBlock = ::ChainActive()[std::min(state->pindexBestKnownBlock->nHeight, ::ChainActive().Height())];
    }