The server is what verifies hit detection and if the server said that someone won then they won, arguing against that is kind of like arguing against a calculator on a math problem...

This is just not true, I've been in tons of spars where a player hits the other a frame before and they get the win because spars do not immediately end when the last hit is landed
There's a frame delay before the spar ends, which is obvious when you consider that you can see several frames of the death gani, that allows for both players to be hit in a certain time frame, but one of them will clearly land the hit first

There are situations where both players hit each other on the same frame but this isn't one of them