You don't need a transaction to be routed by many nodes: how quickly it propagates (and thus how quickly it gets included/confirmed) just depends on how much hashing you do before sending it.

The halving penalty on work just forces attackers (who have +1 routing hop compared to honest nodes) to double the work of those honest nodes if they wish to outcompete them in producing a longer chain (i.e. no 51% attack).

It also allows users to respond to attacks in real-time by affixing harder proofs to their transactions, increasing the attack-cost on the network in minutes should anyone try to pull off the sort of gambit described in the linked page.

Not unless the block sizes down, or the block times/ block/transaction relaying latency go way up. The great firewall of China might cause some issues, but in theory it should not get worse.