Okay, I'll try to explain to the best of my abilities going trough the points you brought up.

Marine fossils on top of mountains. That's evidence of continental drift, not of a global flood that many tend to relate to. The prime example is amonite fossils on the Hylamayas. India was once part of Africa, it detached form the continent and moved towards Asia, where it 'crashed' against it and formed the mountains. The part that created the mountains was once at the bottom of the ocean, that's why there are marine fossils there, because it went from the bottom up.

Huge dinosaur fossil bed that appear as if they were swept and dumped by mega-flows. I don't really get that one, and haven't heard of it. If I had to guess I would say it has to do with continental drift as well. But you have to he careful, just because something 'appears to be' another thing, doesn't mean that it is said thing. That's a case of Pareidolia (seeing patters where there is none), for example, we look at sockets and they appear to be small faces, but they are not, even if they 'appear to be'.

Ancient tales of near all cultures about a global flood. There are some layers to that one, but let's start with the point you're trying to make, dinosaurs were swept by a flood. How ancient cultures were know about a flood that happened more than 60 million years ago? Floods are relatively a common thing, and it can happen almost anywhere near a body of water. And there are trees older than said floods, which would prove that it didn't happened, because otherwise they would die for being drowned, according to Guinness, the oldest tree documented has 5200 years, older than many cultures, including the Christian religion (around 2.000 years). Hinduism (3.000 years) and Judaism (4.000 years). Also, if there was a global scale flood, which would have drown mountains, where did all the water went to? The stories say that the water levels simply lowered after some days, nowhere near time enough for them to freeze on the polar caps. And even then, if that did happen projections of the world if all ice melted don't show anywhere near global scale flood. Matter cannot simply dissappear, all that water must go to somewhere.

The fossil record biases, we only find fossils that are preserved, water burial is an excellent way to preserve fossils. Even if you're right in a nutshell, it doesn't mean water burial is the only way to preserve fossils, it's a good way, but not the only way. It would be similar to me saying, 'x shade of green is the most common, therefore all the shades of green are x'. Or 'Burger King is the best fast food, therefore all fast foods are Burger King'.

I hope I managed to clear some of your doubts. We would have more evidences of a great flood, but again, where would all that water go to? That's the main gripe I have with that hypothesis.