I think you're missing a step, which is where _you_ answer if web scraping can be a viable business model. You're attempting to convince VCs with logic (and a few assumptions), but there's an easier (or harder) way to do it... convince them by making money.
Most VCs aren't ideologues, and don't have an opinion about business models. They will be convinced if you simply show them you're making money. It's not their job to decide if an idea can make money or not; that's your job as a founder.
I applied to YC twice. The first time we spent the 10 minutes talking about if it could make money or not, and never got anywhere good. We got rejected. The second time we were making money, the conversation was smoother, and we got in. It's so much easier to be able to replace "I believe" with "our customers believe". It changes the conversation completely. You don't need to be making billions of dollars; just enough to show that people want what you're making!
tl;dr You're trying to convince VCs when you need to be convincing customers!
(For the record, a lot of what I said here is very money-driven and that's not how I build my company. However, in the context of VCs, which are purely financially driven, it's how you should be thinking about it.)
Good luck, and let me know if I can help! My email is in my profile if you want to talk!