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 (inv.IsMsgWtx()) continue;
            }
            if (inv.IsMsgBlk()) {
                const bool fAlreadyHave = AlreadyHaveBlock(inv.hash);
                LogPrint(BCLog::NET, "got inv: %s  %s peer=%d\n", inv.ToString(), fAlreadyHave ? "have" : "new", pfrom.GetId());
                UpdateBlockAvailability(pfrom.GetId(), inv.hash);
                if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
                    
                    
                    
                    
                    
                    best_block = &inv.hash;
                }
            } else if (inv.IsGenTxMsg()) {
                const GenTxid gtxid = ToGenTxid(inv);
                const bool fAlreadyHave = AlreadyHaveTx(gtxid, m_mempool);
                LogPrint(BCLog::NET, "got inv: %s  %s peer=%d\n", inv.ToString(), fAlreadyHave ? "have" : "new", pfrom.GetId());
                pfrom.AddKnownTx(inv.hash);
                if (fBlocksOnly) {
                    LogPrint(BCLog::NET, "transaction (%s) inv sent in violation of protocol, disconnecting peer=%d\n", inv.hash.ToString(), pfrom.GetId());
                    pfrom.fDisconnect = true;
                    return;
                } else if (!fAlreadyHave && !m_chainman.ActiveChainstate().IsInitialBlockDownload()) {
                    RequestTx(State(pfrom.GetId()), gtxid, current_time);
                }
            } else {
                LogPrint(BCLog::NET, "Unknown inv type \"%s\" received from peer=%d\n", inv.ToString(), pfrom.GetId());
            }
        }