Currently, I find much of the older Warframes suffer from one of five problems if not all of them.
One that isn’t very common is when the frame is Mod-costly, meaning the frame takes up too much mod space for little change to the battlefield. This is still not as much a problem with most frames.
A more common problem among older frames are lack of synergie. This particularly is relating to synergy of a Warframes ability and it’s other skills. (I’m not referring to synergy’s with mods as this is a completely different issue).
Abilities simply being out dated and out shided, this is probably one of the biggest complaints from the Warframe player base in my experience. Having your favorite frame out done by another frame doesn’t sit well with any player. In the case of one frame a companion can do the same thing leaving him in the dust.
Difficulty continues to be a battle for DE as does scailing, naturally some Warframes just can’t do stupid damage in high tiers. However, this doesn’t mean they don’t scale to a degree. My best explanation is, “how do they affect the battlefield at higher levels?” if the answer doesn’t ring decent tune then often it doesn’t matter, some crowd control is still C.C. but if it takes 10 waves of enemies to build, it might not be worth it. (main example referring to frost’s snow globe ability).
Finally, we have the biggest problem which is lack of fun, Though this isn’t common or as big a problem with most of the frames is still a problem with some frames. Granted, some frames hold a different playstyle to them that may be unappealing to a few players. However my best test for this simply is to remove all the mods, augments, arcane enhancements, companions, etc. From the frame and play them in a low level mission. If it doesn’t feel fun then it wont be that much better when you put more mods on them.
Using this info above I compiled a list of frames I feel suffer the most from these problems.
Nekros: synergy, lack of fun, Mod-costly, outdated and out shined (by a companion specifically).
Wukong: lack of fun
Ember: scaling, Outdated and out shined, lack of synergy
Vabaun: outdated and outshine, lack of synergies
My list will stop here however it will probably continue with other player feedback. This simply is a request that DE look over some of the older frames to keep up with the current times as the game evolves. An easy representation of De needing to do so can be seen in Nekros’ warframe profile. He simply doesn’t manipulate souls to the degree that he needs to in order for it to justify the quote from the lotus. All he does is pull loot and bring back the dead, his first doesn’t let you keep the soul, you cant charge your fourth with it and overall he suffers from all the above. Loot may still be loot however I’m starting to draw a line between resources and loot. Considering all the open worlds can’t even be touched by Nekros’ skill.