[thejeff]

There are a couple of early game thugs builds that work well with a bodyguard. A single one with the same movement will split the attacks on the main thug in half.
Vanherse with a Van, Eagle King with a yazata, a few other things.

I'd strongly hesitate to send a Thug with enough bodyguards to trip the 75% hp retreat, unless they're close to as tough as he is.

Later in the game thugs and SCs are often teamed up or used in larger armies. Multiple thugs can be used as SC killers.

SP is different from MP in many ways. Strategies that work in one don't work in the other. The AI tends to recruit more chaff troops and have them wandering around it's backfield and it tends to buy a decent amount of PD. It also doesn't know how to target a thug's weaknesses. This combination means that cheap disposable thugs tend to get overwhelmed, but it also means it's worth investing more since if you equip a thug to handle an arbitrary amount of chaff and your enemies common magic, he'll survive indefinitely.
In MP, if you put that much into him, a player will find the weakness and kill him anyway, so you want minimal investment. Which is ok, because players, knowing that any PD can be killed by a decent thug don't bother investing in much of it and you can raid them with even cheaper thugs. Who will quickly be killed, but who cares they were cheap.