1. The distances from Valleyhome to Redshore are much shorter than the distances from the Lowlands to Valleyhome. It doesn't add that much overhead to the travel distance they already have, especially for the longer distance minors.
2. We're already in the Lowlands but we don't need to make it worse. Vassals have only a
chance of causing a stability loss compared to our Periphery states which have a guaranteed stability loss. This is not a cascade collapse. Our periphery states are more of a threat to us than the Lowland Minors (Northwest). Please stop mixing up periphery states and vassals. They're not the same.
3. Not quite a lot. If we're going to be in an infrastructure phase, we're going to be using Infrastructure policy which means that it takes a turn or two if you count generating resources. It's 8 progress for aqueducts we're going to have to build anyways, since Redshore is most likely going to be our naval trade hub and end up as a True City regardless of our choice.
Building in Valleyhome is going to uproot a ton of people and cements it as even more of a political pit. The other provinces have a hard enough time getting political power and we don't need to make it even worse.
I also don't see why people are latching onto the
extreme long term aspect when it's also better for us in the
short term. The periphery states and provinces are much closer to Redshore than Valleyhome and they're the ones we administer and distribute to centrally. We only marginalize the Lowland Minors who we barely even manage. Remember, we're not the center of government for the Lowland Minors. They're a decentralized scattering of villages.