Wizardry 1-3 are before UO by about fifteen years; Ultima V predates it by nine years. Temple of Elemental Evil is actually the only example I listed that's newer than UO.
Rogue was far from the only popular roguelike; I just went with the earliest example. If it makes you feel better, replace with ADOM or Angband, both of which will almost never throw unwinnable games at you.
JA2 was able to get away with "start of combat" ironman because its start of combat save was before the start locations of every soldier were finalized, because the maps were fixed and revealed at the start of the fight, and because enemy AI was a lot less predictable. Also, JA2 used pre-seeded rolls, so saving and loading wouldn't help you get around the RNG. Xenonauts puts its combat autosave after the locations of enemies are all decided. Also, unlike JA2, in Xenonauts, you're not supposed to know the map layout when you land; figuring out where the UFO is is a part of the challenge (and knowing where the UFO is means you know where the enemy force is concentrated...); and the AI in Xenonauts is very predictable compared to JA2. I'm not speaking in theoreticals here -- on my first game of Xenonauts, I wasn't going Ironman but was limiting myself to autosaves, and found that whenever I reloaded that auto-save after a mission went south, it was completely trivial because I already knew where every single enemy would be and thus could rampage across the map with total impunity; once I realized this, I just stopped that game because it wasn't fun to play like that, and started my second game, in Ironman. On top of all of this, JA2's strategic layer barely existed and was just enough to act as the glue to hold things together; Xenonauts's strategic layer is a real part of the game. Finally, JA2 is really, really tough about soldier death; you can't lose more than about 2 or 3 dudes over a campaign without it being winnable. Xenonauts lets you win with casualties in the hundreds. There's a major difference in how forgiving the two games are, which makes a full-game ironman in JA2 somewhat inappropriate compared to Xenonauts; compounded by JA2's RPG elements meaning it throws fewer novel situations at you than Xenonauts and plays more the same between campaigns.
In other words, different games have different modes that are appropriate.
As for the discussion of "consistency vs. skill", consistency is skill. The end. Read the "An Aside on Skill" subheading here: https://kayin.moe/?p=936