The PT was definitely adult
Ah yes, because a cartoon alien stepping in camel poop while an annoying kid yells “Yippee!” is “definitely adult”. Are you sure we watched the same movies? The OT is way more mature than the prequels could ever hope to be.
No I know exactly what they mean. While the OT is very clear cut with the Rebels vs Empire conflict and frequently lighthearted, the PT has a more complex war where the ‘bad guys’ have terrible military leaders but are mostly made up of systems seeking self-determination, while the rise of Palpatine shows how dictators can manipulate a conflict to gain power. These kind of adult themes were completely absent from the OT.
Andor may be exploring the Republic’s darker side as well, since the soldiers on the crashed ship wear a Separatist symbol but are referred to as Republic soldiers by Maarva. I doubt that’s a mistake, the Republic may be up to something extremely sketchy.