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 (most_recent_block_hash == req.blockhash)
                recent_block = most_recent_block;
            
        }
        if (recent_block) {
            SendBlockTransactions(pfrom, *recent_block, req);
            return;
        }
        LOCK(cs_main);
        const CBlockIndex* pindex = LookupBlockIndex(req.blockhash);
        if (!pindex || !(pindex->nStatus & BLOCK_HAVE_DATA)) {
            LogPrint(BCLog::NET, "Peer %d sent us a getblocktxn for a block we don't have\n", pfrom.GetId());
            return;
        }
        if (pindex->nHeight < ::ChainActive().Height() - MAX_BLOCKTXN_DEPTH) {
            
            
            
            
            
            
            
            LogPrint(BCLog::NET, "Peer %d sent us a getblocktxn for a block > %i deep\n", pfrom.GetId(), MAX_BLOCKTXN_DEPTH);
            CInv inv;
            inv.type = State(pfrom.GetId())->fWantsCmpctWitness ? MSG_WITNESS_BLOCK : MSG_BLOCK;
            inv.hash = req.blockhash;
            pfrom.vRecvGetData.push_back(inv);
            
            return;
        }