is it worth to use it? not really. i think a crewmate with your moded gun is way better.
so far, lich can kill things yes, but it's really inefficient. most of them cant be a tank as they will get crushed by sheer number(getting stunlocked to death), only impact lich wont have this issue.
The best one i found that could at least do damage or soak damage and provide crowd control are impact liches and toxin liches with a kuva nukor or kuva Ayanga
Toxin liches are good at dealing damage/ damage amplification(small, but hey at least it can do something) and little crowd control. toxin liches's 1st ability-> overload(oberon's smite), can actually kill tanky unit such as bailff and ambulas(one shot, not consistence if additional enemies near by) 2nd ability-> cursed ground(oberon's hallowed ground), it functions just like oberon's hallowed ground but the issue is the lich just dont use it often and it has low range and medium duration. 3rd ability-> miasma(saryn's miasma), it deals and proc virals but it's only one stack, the damage is well minimal and lich again doesn't use it often(seriously, Panzer Vulpaphyla's viral quills does way better job at spreading viral procs).
kuva ayanga and maybe kuva tonkor, pairs well with toxin lich as their damage output comes close as killing lvl 135 bailff within one min. and yes the percentage of toxin damage bonus matter.
impact liches are good at soaking damage. it's 1st ability(only this one matters, the others might as well not be there) is carapace(rhino's iron skin). this ability basically turns impact liches invinicble towards damage and status proc(no getting stunlocked, guarantee to continue to fire its gun), it doesnt seem to function like iron skin as it doesnt have a health of its own and its based on duration. i couldnt manage to find the specific numbers of its duration but it's longer enough to make u feel it lasts forever.
kuva nukor pairs well with impact lich as it has a base of 50% status chance and pinpoint accuracy as a beam weapon, making it proc radiation and impact constantly as well as consistence to stagger and confuse the enemies up to the number kuva nukor can chain to.
most if not all kuva liches dont use their 3rd ability often and most of them rarely do anything significant, what matters here are really their 1st ability and the bonus elemental damage+ the weapon they spawned with. And only kuva nukor and kuva ayanga manage to provide some assistance/make a difference.