Another English idiom is "show me the money". Or you could simply say "Prove it." I'm belaboring the point here, but I want to be clear the "Where's the beef" is not just "You're wasting my time, get to the point" but also "I don't believe you, can you prove what you say?"

The idiom is not really "What's the point" but more like "Where is the substance behind your claim?" Anybody can talk a good game, but talk needs to be backed up with action or facts. I don't know if there is a good German idiom for that, or if any of your alternatives express that clearly.

möchte is actually cognate to English "may", so it's pretty soft in the demand spectrum.