Do hard money loans not really exist much that lend based on the ARV?

I'm toying with an idea for a system that would handle guest communication workflows using AI, analyze the feedback, and also trigger surveys post-stay/review for tracking performance.As far as I can tell, there's nothing out there that does those 3, but perhaps there are separate services that provide some or more of those.

What are the key differences in approval times and application processes between private money lending and traditional bank loans?

The reality is the opposite - if it's not in writing then the PMC doesn't have to provide the service or can charge extra for it!

Some DSCR loans out there will also allow a similar down payment.

If the answer down the road changes and you don't notify your insurance provider that could cause an issue if there's a claim.

For those who qualify though, it's the best loan option out there. 

What are the drawbacks compared to a conventional loan?

You may want to use listing spark- which will provide MLS (and other marketing sites) exposure for a fee.

One thing you can also do is work as loan Broker for Investment properties, there aren't any age requirements, reach out to me directly if you are interested.