Assassination missions in Warframe fall into three categories: bosses that have invulnerability phases, bosses that die to a stiff breeze once their time-gating phases are over and the Sergeant.
For example, Lt. Lech Kril, the boss on Mars, forces you to shoot little pipes when he does specific animations, being invulnerable until he does said animations. Once you get rid of his magic shield, he has normal health and dies pretty quickly. Or how about Captain Vor? You shoot him, he goes invulnerable and regains his health, then you shoot him again.
Grineer bosses mostly work the same way. Corpus bosses have some variation, but they all die pretty fast. The Raptors have high damage attacks and require you to drop explosives into shafts, but they die insanely fast to a semi-competent squad. Alad V can’t be killed until Zanuka is killed but Zanuka dies insanely fast as well. The Ambulas fight isn’t too bad, but you have to stand around defending the Ambulas for ages.
The massive Eidolon and Orb Mother fights aren’t much better. Once you’ve taken out the Operator-only shields or the specific-element-only shields, both types of boss fall like flies.
But all these bosses have something in common. You can’t use Warframe abilities on them. Mostly. All Warframe bosses are immune or resistant to Warframe abilities. You HAVE to use your guns.
Some abilities sort of work. Your basic elemental ability will do some damage, which is mediocre if you use Ember, whose heat damage is resisted by most bosses but works really well with Oberon and his radiation damage. Crowd control abilities work for the first cast but each consecutive cast works less and less. Trinity used to be amazing at killing bosses with both the finisher-damage-based Well of Life/Energy Leech combo and the Abating Link/self damage combo, but both were nerfed. The only real boss-killing abilities belong to frames with weapon-buffing abilities. Chroma rules, and Rhino follows closely. Just looking at Eidolons and Orbs, weapon damage wins out every time and really the other frames are there for healing and crowd control.
Honestly though? I would love to see a boss that can only be damaged by Warframe abilities. Because we control these terrifyingly powerful monsters and we only really use them to shoot guns.
How would such a boss work? I have no idea. They would have to have a huge amount of health though, because Warframe powers tend to scale further than guns do. But also, not every frame as a high damage ability, so there would need to be something for everyone.
While I used to say how I disliked Trials, they did in some parts require multiple frames to do specific roles. Crowd control, healing, loot-increasing, protection and speed were all required to do Trials. The problem with them though was that they were complicated messes that often bugged out, being completely inaccessible to newbies. At least a newbie can shoot at the Profit-Taker.
But sadly, I don’t think we’ll ever get a boss like that. Everything in Warframe tends to lean towards using guns over using Warframe abilities. Which is a shame when there are so many Warframes to choose from.