Talos is one of the Imperial nine, though, not necessarily part of the original Nord pantheon (which has been mostly forgotten). The Nords were pretty happy with the Empire in general until the Aldmeri conquest.
It sounds more like you are looking for things to complain about. Bethesda has sub-par writing, yes, but I doubt that sub-par writing directly stems from Bethesda thinking its players are dumb.
Certainly Talos wasn't part of the original Nordic pantheon, seeing how that predated his existence by thousands of years. I suppose the fact that Talos is a favorite son of Skyrim explains his popularity there, but I think it wouldn't have been too hard to maybe extend the Thalmor's hostility towards his worship to the rest of the non-Aldmeric gods as well. In general, I find that the more unique and different a culture is, the more interesting it is to explore. The Nords turning to the Imperial pantheon between games made Skyrim just a little bit less compelling.
Brandon Sanderson wrote on this. He called it Hard Magic and Soft Magic. Harry Potter, as noted, uses soft magic meaning that it doesn't follow many rules. With a soft magic system, the reader is left with a wider sense of wonder because literally anything can happen and be explained by magic. Other soft systems include "A Song of Fire and Ice" or any Dungeons and Dragons book ever written. This style leaves stores very prone to fall into deus ex machina traps for solving situations.
Other side is hard magic systems where everything is explained in great detail. Wolverine's magical powers are an example of this. He has magic claws and magic healing powers and they are pretty well defined. He can't, for instance, start flying for no reason and explain it as magic (or mutation in this case). Stories of this type will more often let the protagonist solve their problems with their magic without it feeling deus ex machina-ish.
Now, Elder Scrolls, as well as most fantasy games, strikes and interesting duality between the two. The character you play operates under a very strict hard magic system; you can't just start doing something that your class can't do. Yet, the NPC's are able to preform great feats of magic well beyond the scope of a players abilities. NPC's often possess a strikingly powerful array of magic abilities that PC's at a much higher level can't obtain. How often have you stumbled upon a ruined castle in a game and found a necromancer 20 levels below you that moved into town, turned the common folk undead, and now commands an entire dungeon of ex-townsfolk minions (of something of the ilk) and wonder why you can't do that?
Well, the why is easy, it's OP. But the sacrifice here is loss of flavor in lieu of a bigger and more wondrous magical world.
I agree with all of this. However, I think it's fair to point out that at least as far as the background lore and worldbuilding of TES goes, new additions are largely built on the foundations that previous games (and even Kirkbride's weird OOG ramblings) built, leading to an expanded world that feels much more "plausible" and satisfying than many other fantasy franchises. To continue picking on Harry Potter for a moment, the problem with the new information about magic that each book provided was that it was all disparate. We would learn about Spell A, and that was it as far as Spell A went. Then we would learn about Spell B, and Spell C, and so on. There was no real connection between them in the greater world of magic. Not so with TES. Now, returning to
The Remnant of Light, we can put it into a bit more context by also looking at
this book. Consider:
The spike of Ada-Mantia, and its Zero Stone, dictated the structure of reality in its Aurbic vicinity, defining for the Earth Bones their story or nature within the unfolding of the Dragon's (timebound) Tale. The Aldmeri or Merethic Elves were singular of purpose only so long as it took them to realize that other Towers, with their own Stones, could tell different stories, each following rules inscribed by Variorum Architects. And so the Mer self-refracted, each to their own creation, the Chimer following Red-Heart, the Bosmer burgeoning Green-Sap, the Altmer erecting Crystal-Like-Law, et alia.
...
[t]he arch-mage Anumaril fangled an eightfold Staff of Towers, each segment a semblance of a tower in its Dance. And then seven of these segments were borne by White-Gold Knights to distant Fold-Places, where they were hidden.
Remembering that
Remnant began with this Anumaril giving Filestis a Remnant of Light and asking him to take it to the "cold sunset limit of Tamriel" (probably Skyrim), it seems safe to conclude that the Remnant was one of the eight pieces of the Staff of Towers. And if the Towers can dictate the reality of the surrounding area, then it makes sense to suppose that the fragments of this magical staff, based on the Towers, can too. So, the changed climate of High Rock wasn't just something that the writers pulled out of their asses, but a natural extension of Tower lore, which has its roots in games like Daggerfall and Morrowind.