While your analysis is correct, I don't think the seller is going to consider your opinion. They need to sell at the sale price, or else they wouldn't have put it up there at that price. It's probably at market value.
They may be wrong, their house may be unlivable, their expectations aren't realistic -- but they haven't changed the asking price to convey that. I don't think it hurts to put in an offer, but some agents won't even bother.
I do not recall which savvy investor said it, for some reason I think it might have been @Russell Brazil (sorry Russell if I tagged you incorrectly), but he led a response for someone with a similar problem; their offer was so much lower than asking and the investor was upset their agent either wouldn't put in the offer, or that the seller wouldn't even consider it.
Point being that just because your analysis may be correct, the analysis may not be accurate for the area or property you are trying to buy. If crappy homes can sell for 280k and the ARV is 300k, then prepare to pay market value, or don't plan to play in that market.
Now, counterpoint, if comps in the area suggest your offer is fair, then by all means, continue forth. You're just dealing with an incompetent seller or agent who put the house up for sale for an exorbitant amount, but I don't think there are many cases of that.
Rehabs tend to be similar cost (depending on finishes) in a 200k house as they are in a 400k house. A new kitchen may be 30k in a 200k, and 40k in a 400k house, for example. Why not find a distressed property in need of full rehab at that cost where you can bring the value up to ARV, not something that only has 20k room and needs a 65k rehab, where the seller won't sell it to you anyway? It just seems like a lot of things not working in your favor -- you're trying to jam a square peg into a round hole.