Hello DE. I will be very synthetic and brief. Your game is in a sorry state. The word that best defines the feeling is "abandoned". If I analyze point by point the great divisions of Warframe, I find:
Lunaro: Unnecessary. Clarification: with "unnecessary" I refer to the content that is only played by a minority, content that does not enrich or improve the main content of the game and also, which was valuable time and resource development by DE that could have been invested in improving other essential plots.
Conclave: Unnecessary. Clarification: with "unnecessary" I refer to the content that is only played by a minority, content that does not enrich or improve the main content of the game and also, which was valuable time and resource development by DE that could have been invested in improving other essential plots.
Sorties: Trivial and repetitive content. Clarification: They do not provide a real difficulty, the value of the rewards is debatable and in general, it feels like an automated system only in order to "give something to do".
Arbitration: Trivial content. Defective implementation due to periods of invulnerability for enemies. Clarification: To make enemies immune to bullets, is NOT real difficulty. It's just an annoying, cheap mechanic and offers the feeling that you do not know how to balance the game or how to design really challenging and fun game modes.
PoE: Actually, it's not an open world. Dispenseable content. Designed to be "mandatory" to play, with the addition of resources and objects independent of the global economy system. Clarification: by "dispensable" I refer to a content that is independent of the main content and that is not properly interconnected with the economy / resources / main history system. The current "open world" is just a gigantic map with its own micro-game.
Fortuna: Actually, it's not an open world. Dispenseable content. Same problem as PoE. Clarification: by "dispensable" I refer to a content that is independent of the main content and that is not properly interconnected with the economy / resources / main history system. The current "open world" is just a gigantic map with its own micro-game.
Solar map missions: Repetitive, monotonous and too easy. All mission types (perhaps, the "concept" of mission itself) need a complete reworking.
Weapons (primary, secondary and melee): The riven mods have not made the less used weapons compete on equal terms with the META weapons. The situation is the same as always: only a few weapons are considered for "final game".
Warframes: (Just to mention a few) Wukong, Vauban, Nyx, Hydroid, Atlas ... a lot of warframes are outdated and / or need a complete reworking.
Mods: 90% of existing mods are not used or used very little. A complete re-elaboration of all the mods is necessary in order to make them viable in different META compilations.
Mods riven: They have made the best weapons even better, they have not made the worst weapons better. The cause is a defective design of the concept of "improvement", as it is to increase a 200% probability of state in a weapon with ... 5% of base state.
Focus: 90% of everything that can be used in Focus is unnecessary, it is poorly designed and does not contribute anything especially valuable to combat with the Warframe. A complete reworking of the Focus system is needed.
Syndicates: No update or improvement since its launch. Abandoned content. 90% of the union mods are totally dispensable. The unions are just another "Focus", a store where we exchange points for "things". The unions need a reworking.
Pets: Kubrows and Kavats (especially), they need a reworking of their AI. It is necessary to change (or completely eliminate) the annoying system of cryostasis in order to facilitate the change and choice of companion. New mods are needed for them and new "breeding" options.
Archwing: Other content that feels independent of the main game, another micro-game with its own maps, weapons and resources. Archwing is another example of development time invested in something that feels half-finished. It's like playing "another warframe" inside Warframe.
Lotus: Oh, Lotus... How long have we had a ... hologram? One year? A whole year without developing the story or outcome related to Lotus. It seems a "small detail", but it is not; It is a representative sample of your attitude, DE: launch new content and then abandon it for years.
Archwing, PoE, Fortuna, Conclave, Lunaro ... DE, you have invested so much time and effort in things that only play a minority. You have created "in-game games", things that we can play within Warframe, but that are not part of the main Warframe content. And all that time of development could have been invested in improving and balancing the real game: our weapons, warframes and pets, missions in the solar system, LORE, focus, syndicates ... thousands of lost hours that have not served at all.
Maybe, DE, it's time to stop and reflect on what you want from Warframe.
In general, the current state of Warframe is summarized in one sentence: only suitable for noobs.