I've always felt that doctrinal units should be built. That gives a lot more control over their balance via build time and tieing up production and resources while it's built. It also eliminates the "panic" call in where you instantly have a unit if you need it
I'm pretty sure that this used to be the case. Except the units got replaced. Supposedly penals were literally a "placeholder" for elite troops, (Meaning you'd have to tech T1 in order to get Shocks or Guards, and once you picked a doctrine you couldn't make the stock version any more.) that's the reason they weren't given a purpose for a long time if I understand correctly.
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