Kinzhals are just air launched Iskander short ranged ballistic missiles. Russia calling them hypersonic weapons is technically accurate but misleading, as when people refer to hypersonic weapons they typically refer to weapons capable of sustained and maneuverable hypersonic flight within the atmosphere.
Patriot PAC-3 interceptors are literally designed to shoot down SRBMs, it's a primary use case. Many fundamental aspects of their design such as using (pseudo) hit-to-kill interception instead of a more normal blast fragmentation warhead are consequences of this focus. It's not surprising that this happened once Ukraine got modern Patriots.
And it might not have been in "hyper-sonic" mode either. It could have just been cruising on its way to the target before it began its hyper-sonic descent.
Afghanistan-lite? The Ukraine situation seems much worse than Afghanistan.
Re regret, I guess it depends on who you mean by 'Russia". Looking at their faces I think most Russian top officials apart from Putin were rather horrified from the start.
It can't afford to. It will be instantly recognized as an admission of weakness in the snake lair.
For as long as Putin's regime stands, klepto elites around him will be sure that, at least within Russian borders, they are still kings, and they can live the rest of their lives surrounded by long legged mistresses, and drowning in luxury.
If Putin is seen as weak, any small time gang will think that moneys, and power of Russia's top oligarchs are for grabs. It will be then, when a preemptive coup attempt can happen.
Patriot PAC-3 interceptors are literally designed to shoot down SRBMs, it's a primary use case. Many fundamental aspects of their design such as using (pseudo) hit-to-kill interception instead of a more normal blast fragmentation warhead are consequences of this focus. It's not surprising that this happened once Ukraine got modern Patriots.