Faction strengths?

[Centurio Nixalsverdrus]

The Hypaspistai I generally use to attack, not hold the line. Thorakitai and Phalangitai hold the line much more cost-effectively. When it comes to attacking the sword is much better than the spear, and it's exasperating to watch my units switch to spears during a prolonged melee (or even worse during the charge.)

They always charge with spears and that's indeed useful as I was informed long time ago.

I mean, if you have such high lethality long swords, why in the world would you bother to hold the line?

This sentence doesn't make much sense. So if you've got a longsword, you don't hold the line? Holding the line, keeping formation is essential for surviving and subsequently winning the battle, although I admit they would perform much better with spears when holding the line.

As I'm in a Seleucid campaign right now, I can choose much better elites than the Hypaspistai, namely the TAB and the Peltastai Makedonikoi. They're better in their roles of line holding and attacking (Peltestai have an added option of flanking utilizing that extra stamina), respectively, and have defense values suitable for their job.

Peltastai Makedonikoi are much better suited for attacking than for holding the line. Hypaspistai are excellent at holding the line. They are basically excellent in any job that doesn't consist of running around. As are Kuarothoroi etc.