I can’t be arsed to troll eBay for another deal, and then fork over another $100 for a DA caliper that may or may not work.

i used to live in london and use ebay a lot. you can easily set a very specific search, and create an email alert when something matches your criteria. was working very well.
And i was using a bid sniper as well, bidding automatically at the last moment.
Made using ebay super convenient, as long as you're not in a hurry.
I bought a campag bora one front wheel for 100 pounds, back in the day. new.

Yes. They're only selling off leftover stock. No explanation as to why.

Feels like everyone on this forum on a 218 had a cracked frame at the seatpost area. Given VB margins, they can't be profitable selling models that are constantly creating warranty problems.
Plus the fact it's an obvious clone of Pinarello, which I assume has resulted in Pinarello contacting VB, one way or the other (and/or the factory they source from).

I guess it would be pretty straightforward to create a questionnaire that would fill in a simple database with important metrics. Without knowing your age, weight, measurements, flexibility and so on, we're shooting in the dark, as you didn't write much in way of context.
The Triban RC520 is pretty crap, it's not just in your head.
Assuming you're young enough, either flexible or willing to get flexible enough (not that hard), i dont think you need to overthink it too much, the VB 268 will probably be life changing, and you dont need to spend more, especially if you order it black. To customize, you can get decals cut locally (or via aliexpress) for cheap, it's a good way to save 100 usd.
Given your budget, you should assume you'll be your own mechanic going fwd, because labour cost post inflation & now that bikes are fully integrated can double the cost of the bike in a few visits to the LBS... You'll also learn a ton.
Expect to start with all the spacers on the 268, because that decathlon bike has a VERY relaxed geometry. Then you may find yourself removing spacers over time, which will mechanically go faster on the flat. From this perspective, make sure to buy a cockpit that allows to have spacers above the stem, otherwise you'd have to cut the steerer every time, which is a disaster. It would also be pretty smart to get a bar & stem vs cockpit, because you may also want to change stems.
From a bike fit standpoint, given the uncertainty, you would benefit from a bike that is NOT fully integrated, to allow making changes more easily.
Changing anything on a fully integrated bike is absolutely miserable.
The best bike is a comfortable one that fits you.

VeloBuild  268  in size Medium seems like it would be a good option coming at under my budget.
I compared also the Hyggee but the Velobuild seems to be a higher QC frame

I'm considering a budget of $700 USD for the frame alone. Are there any options in this price range other than Velobuild? I've also seen the Hyggee frames selling for a bit less than that, but I believe the Velobuild quality control might be better.

I plan to repurpose my Mavic Krysium wheelset that I've used on the Triban until I save up for a carbon wheelset. As for the groupset, I'm thinking of going with the Wheeltop EDS-TX.

I haven't budgeted our the rest of the build or components, as I wanted to start from a frame and go from there.