I think you're giving clone!Palps
and the Vong both a bit too much credit.
Clone!Palpatine was obviously more than a little insane (probably from imperfections in the process for cloning Force-sensitives, combined with whatever mind-bending experience he went through as a disembodied spirit), and didn't seem to
have a long-term plan beyond "Let the Galaxy burn!" And I never got the impression he thought of the Vong as a particularly serious threat. Sure, he was happy to use them as an excuse to hyper-militarize his Empire, but they never seemed to factor into his plans all that much, or he probably would have set up a network or Outer Rim listening posts and fleet anchorages expressly positioned to repel extragalactic invasion. It was well within the Empire's capabilities to do so, and it would have fit Palps' narrative of prepping for invasion quite handily. But he never did it, which leads me to believe that he never saw the Vong as anything more than a convenient excuse to claim more power.
Similarly, the Vong seem to have
barely understood the galaxy they were invading, even after 50 years or so of active infiltration. The only people among them who seemed to even understand that there
was a difference between the Empire and the Republic were the smarter, more experienced spies like Nom Anor, who learned this by personally interfering in the Remnant's politics in the wake of Operation Shadow Hand. Overall, their infiltration "plan" consisted pretty much entirely of "divide, distract, and incite", still with very little overall understanding of the enemy they faced.
If they had truly understood how the New Republic operated, and assuming that they needed to start on the Rim instead of simply bypassing it "above" or "below" the galactic plane, they would have done things
very differently. Their best bet would have been to use every ounce of the element of surprise and their early technical advantage by striking at Dac first, then charging up the Perlemian, taking out major industrial and ship-building centers along the way like Lianna, Abhean, Roche, Lantilles, Axum, Alsakan and Coruscant. Then, with an unprepared, under-defended Coruscant conquered, they could focus on ravaging the Core and Colonies.
If the Vong's leadership had the
slightest understanding of galactic civilization, sacking the Core would have absolutely been priority #1, not diddling around the Outer Rim for two years, seizing territory that looks really impressive on a map but ultimately doesn't impede the enemy all that much.
