According to Einstein the speed that gravity acts is the speed of light. But in gravity time slows down and as Einstein has said where time slows down in gravity so does light. You would have to wait for it. So if light slows down then the action of gravity would too. I believe this would prevent a black hole from existing.
The equations of GR take into account things like the difference between observer time and proper time and how space-time curvature alters the behaviour of the change of space-time curvature. You're not suddenly having a flash of inspiration demolishing GR, it's all part and parcel of the theory already and the theory predicts black holes.
Infact, Penrose and Hawking showed that for any reason space-time, singularities are inevitable.
Even if your comment about gravity slowing etc was correct, without explicit calculations you'd have no way of knowing if the knockon effect was enough to prevent black hole formation.