I disagree with the points presented, and I understood your frustration until the "Flag on Play" replies. I know this is a complete conjecture on me reading the emotional subtexts in your responses but this is a strange hill to die on.
Warframe is a videogame. If you love Railjack gamemodes, then I thought this kind of thing would inspire you to build your own? I remember at launch, before the rebalances and bugfixes, riding with a good host left me so bedazzled that I began work to build my own RJ, and riding with weaker hosts gave me fuel to continue my own progression through more difficult missions, Intrinsics leveling and Valence Fusions. Now the boot's on the other foot and I can host public missions, and even the times where nobody joins and I just complete a Skirmish by myself I'm having a blast.
You can also just. Avoid playing Railjack, should you find it annoying. The only content it locks you out of is The New War Main Quest (which level scales to your equipment anyway and needs you to own an Amp and a Necramech as well) and the Call of The Tempestarii Side Quest (Sevagoth Main Blueprint). I apologize if I sound insensitive but I can't relate to taking the stance of locking all other players over scaling restrictions when you have the means of overcoming them by yourself (which in itself, has been really exciting and rewarding in my personal experience).
Honestly, I think it might check out in lore. In the same way that the Warden resembles Ballas but doesn't look exactly like him, as he is a Conceptual Embodiement of Kullervo's guilt, the Kullervo we fight in Duviri might be changed in appearance since his fall into the Void. Same way Teshin, and, well, every outsider that landed on Duviri changed their appearance one way or another.