Cancellation would be a bad idea. That would give the image of hiding in fear and the new stories for all be about how Ukraine made it too dangerous to conduct a parade because it would be attacked. It would be cast as a big Ukrainian victory. So instead, you scale it back, all the same guys in the reviewing stand, flybys, a single symbolic World War II tank comes by to remind people about fighting Nazism. It’s actually a pretty brilliant plan. Probably the only improvement on it would be if they put a couple of damaged leopards, challengers, and M1’s on flatbeds and pulled them through the Square.
I like your idea of using the parade to show damaged military equipment from the war in Ukraine.