It's actually thought that Kessler syndrome is kind of already happening right now, which is why there's a lot of push right now to try to de-orbit the very large pieces of debris, so they can't act to form further debris.
The effort of getting a ballistic trajectory that peaks at 500km is a lot smaller than reaching a stable orbit of that height. And just like WWII aircraft you don't need to hit them, just produce enough shrapnel in their vague vicinity.
The biggest hurdle is the universal international condemnation you would receive for such an act
And you can't just wave around "hacking the control plane". Russia's been trying to interfere with Starlink for a while and they haven't had any long term success. And finally, even if the did somehow get access to the control systems at SpaceX, the satellites can't de-orbit quickly. It takes weeks to de-orbit, over which time they could be commanded to reverse course.
I should add that anti-satellite missiles are _large_ missiles. The missiles of this size in the US arsenal are SM-3 missiles (or larger). The number even the US has is only in the high hundreds to possibly low thousands. That's completely out of the ability of Russia. It's maybe possible for China but not in their current stockpiles.
Laser beams are also the replacement for ASAT.