It's not about the targeting computers not being powerful enough. It's about the counter missile not being fast enough and the hypersonic missile being able to zig-zag like a cruise missile, but with similar speeds as ballistic has in it's decent phase.
Then how does it react when the missile is going 3x as fast and sweeps right when the counter missile is sweeping to left towards the missiles previous position and misses, in that case it needs to be faster than the incoming missile itself. Yes, the speed would not be a problem towards a predictable trajectory, that's how ballistic missiles are intercepted even if they go super fast. it's basically a high school math problem in that case to calculate the point of interception in a firing solution. It's also fine if missile can change course, that's how cruise missiles are shot down, because the counter-missile can still race with them when they turn, but when the missile is fast and can change directions mid flight then it doesn't much help how fast the computer calculates if the hardware can't react fast enough. it's basically like if your mind were able to move at superhuman speed but your body is still human and you get shot and only thing you can really do is to watch the bullet approaching but being unable to dodge fast enough.
The issue with hypersonic missiles is that they go so fast that the air around them heats up enough to become a plasma. This prevents radio, microwave, and infrared based comms and radar systems from working. So any proper hypersonic missile is stuck with using either optical sensors (which require a ton of processing power and is slow) or inertial sensors (which aren't very accurate due to drift) in order to plot its course.
The Russians are the only ones with "hypersonic missiles" because they're using a different definition. Theirs are just ballistic missiles that move at hypersonic speeds, which by definition can't change course and have a huge IR and radar signature, so it's not that difficult to set a slower patriot missile to be in it's way to intercept.
Also, if Khinzal was really that maneuverable then how were the Ukrainians able to intercept multiple with the much slower Patriot missiles?
One can put serious doubt on their claims. Ukrainain MoD has every incentive to lie and on top of that they did show off some empty soviet era bombshells as remnants of a shot down Kinzhal.
The car here is moving like 500km/h and it's doing a zigzag in erratic pattern. Even if your rocks can change trajectory themselves mid flight they simply aren't moving fast enough. Oh and you have to hit the car from 1km away.
Your scales are way off, and you're oversimplifying and call-of-dutyfying the laws of physics. Right now you're arguing people about real life phenomenons by talking looney tunes. You're flat out just wrong, and I'm not even going to try explaining why because you just ignore every single explanation anybody else have made for you.
By the way, stop fanboying about a ballistic missile, it's weird and honestly really cringe.
This thread is earily similar to one where I recently had to explain to someone on the ebike subreddit why a bike going 35 mph won't be fast enough to keep him from getting bitten by a dog if it wants to bite him. "No dog can run 35 mph" ..."they don't have to be faster, they just have to plot an intercept course" It's not fucking complicated at all.