Witch is really really good with morningstars
@Boeroer has talked about this build before, maybe he can elaborate.
I can give you the gist, cast borrowed instinct, secret horrors, and use brute force with morning star modal plus spirit frenzy which applies staggered on hit, together you debuff fortitude by like 45 points. The "will" debuff in willbreaker is also good because most of these cipher spells target will. At this point you crit a lot, also could cast some disintegrations and such.
I like barbarian / soul blade for witch personally, not exactly sure the ideal stat spread but have used in the past max INT max PER low dex medium might high con low res. I feel like with frenzy barbarians have such bad deflection they're just going to get hit anyway so I usually dump resolve, but I guess you could also max it (lower con and might some) and with borrowed instinct defenses it wouldn't be that bad. You have pretty good healing once you get savage defiance and especialy stalwart defiance, which at 2 rage can be used multiple times per fight.
On barb side I mostly pick +damage and +action speed passives like blooded, bloodlust, one stands alone, bloody slaughter, blood thirst, and defensive stuff like unflinching and thick skinned. Only actives I usually take are frenzy tree (stop at spirit frenzy, spirit tornado is bugged with stagger procs) and defiance tree, though the shouts are okay.
On cipher side, spells mentioned already but also hammering thoughts, iron will, lingering echoes, draining whip, phantom foes, psychovampiric shield, mental binding, and one charm spell (i usually upgrade as i go along). Only direct damage spells you really need IMO are disintegration, maybe soul ignition, at least if you're a soul blade, because it's generally higher DPS to use soul annihilation
Oh and morningstars have good penetration already, with hammering thoughts and phantom foes that gives you +2 pen so you're effectively at 15 pen legendary, 16 mythic and it does crush/pierce. There's almost nothing in the game that resists crush and pierce at 16+, and even if it did you can use slayer's claw to upgrade frenzy's strong to energized to get 18 pen at mythic, and that will get through everything. You'll also crit a lot which adds 50% pen, so even on upscaled POTD you don't really need devoted. Compared to a witch it's the same pen bonus anyway (at least when phantom foes is applied), so devoted gains a crit bonus but has a bit less accuracy, much less CC, less fortitude debuffs. Devoted is sturdier though, with unbending, and disciplined strikes is a pretty good source for crits. If I were going solo a witch might be tough until you get the defiance tree but in a party the healing is plenty.
I don't know much about warlock builds, I guess you would cast spells to debuff fortitude, otherwise I'm not seeing a lot of synergy there.