The cathedral was falling apart because Vrythur was pulling down fragments of the ceiling with his own power. The video you post to prove this even says it.1) how application of force works. Shockwave spread out all across the body infact the spread out in all directions. They also don't responsed to physical objects the same way. If I punch a door my hand is being stopped by the door. Shock waves will instead flow through an object. It's also important to remember the damge is not focused unlike say when you stab someone. To give an example, a modern day Kevlar vest can stop bullets we even have some that can stop a 50 cal, but if you're wearing said vest and step on a land mind, you're ass is grass. This is because objects are desgined to deal with specific applications of force. Surviveing a shock wave does not mean you can survive bullets. There were people in the shock wave at Hiroshima when the bomb went off that survived, they're not immune to bullets.
2) similarly the feat itself can't be taken at face value. For one the cathedral was already falling apart. In the fight chunks of the ceiling the size of a horse were falling. The buildings structure was already compromised. This immediately cast doubt on how strong the blast needed to be to finish the job. That and because of the nature of shockwaves the DB wouldn't even had to take 1/10 of the energy released.
"The rocks are flying but they somehow directly defy physics to just tumble down the mountain."Nah if you got stuff to do man go do it it's just a silly debate, your life's more important.
I will say this it really doesn't look like those rocks are being sent flying (i did mis this bit on my first few watch throughs so thanks for pointing it out) it looks like they're just tumbling down. They're just doing so from the outside because that's were the blast oginated from. I say this because they don't appear to be moving away as to our eyes they don't start shrinking like objects far away do. (This is seen with stuff like speeding cars)
Serana literally says as such in the video at 2:50 and 4:50-it's not hard to prove here you can watch the fight before the cathedral collapses it's litteraly falling apart at 2:50 and 4:50. Also we don't really know if they went flying or just tumbled off the mountain our vision is obscured and we only see the end result not how it happened. Also again explosions are omni directional he only took a small part to the face.
THAT'S AFTER THE CHANTRY EXPLODED.
Literally how is it possible to be this dishonest?