To start from a bit far away, i think a lot of people would agree that using helminth system to exchange one warframe ability for another is a really interesting concept, that allows some of the warframes to fix natural flaws in their base ability sets.
Even more to it, sometimes replacing base ability allows for some powerfull synergy to take place instead, greatly boosting warframe power way further beyond just fixing a flaw (Ash with Banshee's silence and its augment as example: augment boost finisher damage, Bladestorm counts as finisher damage).
Exploring those possible combinations and synergies is a lot of fun, although that may be a subjective statement.
That all being said, something that prevents me personally sometimes from helminting abilities on a frame is that specific frame identity. I am not talking about some twisted personal role-playing concepts of mine, like "You cant put firewalker on Frost, for he is a cold themed warframe", im talking about warframes that by losing their weakest ability for probably way better one, just stop being that warframe anymore. Think Revenant; Dance macabre is a way to go replacement if you want to push Rev to higher levels, but that leaves you with his mind control, mist shifting and helminth's something, and in a number of cases (which obviously depend on your helminth ability choice) Revenant becomes some another kind of weapon platform frame.
It may seem like a subjective problem. For you, Revenant without Dance macabre may still be "vampire themed" and fun, and no problem here at all, but for me, removing his 4th for better high level efficiency just makes him not Revenant.
WIth some frames, lets say Frost, replacing one of his abilities (and mind you, no one really going to replace already good abilities, like Avalanche or Globe) still preserves Frost's identity as ice controlling, freezing powers fantasy of a warframe.
This is my biggest issue with recently released Voruna, werewolf-not-so-werewolf themed warframe.
To me, first three of her abilities have nothing to do with wolf/beast theme at all, and saying "Well, its actually not her powers, but her severed wolf head powers so its ok", not making it to me. I dont think its a case of me having different expectations either, its just slapping some lore reason behind abilities that would look and work just about the same on any warframe is not adding anything to Vorunas identity.
And there we reach her 4th ability, which sells whole beasty wolf identity/personality quite well i must say. Aside from lacking animation for sprinting on all fours (i know how much work it is to do something like that, do not think that just reusing some kavat animation will do it, considering all the cases of sprint-to run-to idle-to jump-to turn and all of those variations, unless you restrict the movement heavely). Ability has another major but - its horrifically weak.
Power wise ability is the weakest of them all, more so, lacks synergy with any other.
- Its a gapclosing leap in a skill set with another gapcloser leap already presented.
- It locks you of all of your weapons, but most imortantly here, your melee weapon, a weapon that massivly boosted by all three of Voruna other abilities.
- It does not count as melee kill for Voruna 3th,
- it gets only one time damage increase from status effect and not per unique status type like Condition Overload.
- On kill damage doubling mechanic is not triggered if enemy dies from status procs or slash procs, it triggers only if initial hit kills.
- Radial part of damage applies before single target part, making combination with Mark for Death impossible (radial damage procs the Mark first, dealing way less damage)
- Radial part is not even a slash proc, its some weird true damage zone with tiny damage.
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The only thing that kind of works with Ulfrun's descent is her invisibility, which persists through all leaps, but all of the melee buffs that you get after breaking invisibility does not affect Ulfrun's descent either.
In general, its the ability that can kill in regular starchart to extent (it falls fast even there), and anywhere higher its just a way to waste energy and nerf your damage output by locking you of your really well synergising with first three abilities melee weapon. I dont believe any warframe should be that way - ability that contributes to frame identity the most being the weakest one.
Now, you obviously can helminth over Ulfrun's descent many things, that will benefit Voruna way more, being it cc, damage, armor stripping or healing. She will scale way better that way, probably will just be more comfortable to play. But by doing that, she's not a wolf or beast themed frame for me anymore. Voruna is the case, where all of her personality, all of her identity converges in one single ability, and that ability is the first thing anyone who played her will replace.
Tell me you are asking for a buff without telling you asking for a buff post, ngl.