The ATACMS being at their end of service life means that we would have had to spend far more to have them decomissioned properly than to just ship them to Ukraine. That and these nearly 30 year old missiles seem to still be able to get past Russian latest and greatest AA platforms. These being cluster munitions make them ideal for taking out large groups of aircraft in airfields that the HIMARS couldn't reach. Storm shadow cruise missiles are fantastic and have a greater range but they're much more expensive and take more effort to deploy.
no, not really, your options is small cluster warhead with longer range or 3x bigger cluster warhead with less range (the one used in berdyansk), neither of which are effective against armour, and then there's unitary variant, which would require direct or almost direct hit. so no, it's only good against soft targets: aircraft on runways (not in hardened hangars or such), SAM sites, ammo depots, radar installations, unarmoured vehicles, troops in the open and so on. unitary variant might be good against command centers