I do believe you are vastly underestimating how difficult an attack on the bitcoin network would be. I seriously doubt anyone other than a handful of state level actors could pull it off, and even then I am not sure. The amount of energy we are talking is tremendous, and gets orders of magnitude larger the more blocks you go backwards in time. The XVG hack only went back 22 blocks, that is mathematically, and most certainly financially and perhaps even physically impossible with bitcoin. The amount of energy and money spent would never, ever make it worth it.