Are you actually asking to explain you the reasoning behind the addition of Lavinia or are you just criticizing or shocked that people are putting Lavinia where she belongs, in a aggro control deck?
Let me put it this way, while the way to "make her shine" might be in a deck with a bunch of creatures, the most likely way for her to be successful is in a deck that is already powerful, using her as another angle of attack (see the decks from the past week's VSL) rather than in an archetype that hasn't been traditionally successful in vintage, in which it has some dyssynergy with the most previously successful card in the deck in Thalia.
Maybe this is the right shell, but I don't think by any means we should take for granted because Lavinia is a creature with the human type that this is the shell that makes the most sense. As you said "an aggro control deck" might be the best shell, so why not start with the best aggro control deck in the format in Xerox as a home.
@evouga I would caution this thinking. @Brass-Man got pretty unlucky flooding out multiple times in his 20 mana deck with 4 preordains vs some of these other decks running more land and in some cases fewer smoothing cantrips. That can happen, but I think if all these matches played more times, on paper, death's shadow would come out on top against most of them (the exception potentially being the MU he won, against Survival).
I always wonder about decks like this and the potential inclusion of grove of the burnwillow and punishing fire. I know it can feel a little under powered in vintage, but the incremental advantage is quite high, and it seems like you can probably make an opposing control players life very difficult with them, while still getting value against stuff like shops and to a lesser extent dredge. It definitely seems like a thing that could be friendly with 4 dacks.
Yeah this gives me a mix of delver and angler vibe, and I am ready to be impressed. The other somewhat reasonable point of comparison is Bedlam Reveler but UU instead of RR. I have tried to make reveler work in Vintage, though admittedly he has a draw 3 stapled to him.
I think this creature is worth testing.
@desolutionist So will is banned in both formats, which is why it isn't listed above. You can play the rest of those cards though! (We have had a hard time building a storm deck with only necro as the engine, because of the way necro works, if you find a good build please share!)
I think people are not super excited about MTGO these days because of arena. The more people sell out of mtgo the lower the prices get. I think there is a floor, but we haven't reached it. Some cards that are hard to find and old will still gain value over time, but "investing" in mtgo cards seems like a silly idea, since they can reprint anything at any time, and at some point, mtgo is going to go away.
I think it is fine to buy in to play vintage, but don't look at it as an investment.