The only reason the Core sector fleet would be any better would be that
its intended use was defence against another round of 'Barrack Emperors'
and frankly, a fleet that's completely un-used to battle would likely
crumple when a veteran frontier fleet came against it. I don't think
Dulinor being able to defeat it with the Illelish fleets is that
unreasonable, especially if he'd spent the last decade or so shifting
his fleets' emphasis from anti-piracy and small task force actions to
major fleet battles, both in training and (as much as he could without
attracting notice) composition.
Good point.
It does explain the success of the Spinward Marches fleets on kicking out Emperors during the Civil War era. And is entirely consistent with the repeated cycles of Roman coups.
[Lucan] didn't start out deranged, just short tempered, and equipped with a
personality utterly unsuited to the office into which he was thrusted.
The stress of the job got to him, basically. There are plenty of
examples of this in history.
As an interesting alternative, having Lucan START as a spoilt brat, but maturing in office. Unfortunately, by the time he realises what a hash he has made of things, the Imperium is irretrievably broken and his reputation is unsalvageable.
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Cheers,
KenB