A major flaw , I think it is in relativity.
It doesn't. If you're talking about pictures like this:
those are only meant to show the shape of a slice of spacetime. Turning them sideways or upside down changes nothing. All that matters is that the circumference is less than $π$ times the diameter.
I don't know why they are almost always shown pointing down. I suspect that many people are confused by the "rubber sheet analogy" or by the gravity wells at science museums into thinking that turning them upside down would turn gravity into antigravity. It wouldn't. To get antigravity you'd need a shape whose circumference is more than $π$ times its diameter, which would look very different.