The availability of mods is a huge W for Skyblivion. I'm not sure what the appetite will be for Creation Engine modders switching over to UE5. That will hold it back a lot in terms of long term appeal in my opinion.
I'm more worried with the appetite of Bethesda in giving up control of its UE5 creation than the appetite of the modders.
There's plenty
Enderal
The nameless mod for deus ex
Black Mesa
Anomaly, misery, Dead air, Call of chernobyl (Stalker)
Entropy : Zero 1 & 2
Falcon BMS
RallySimFans for Richard's burn rally
FS2 for Freespace 2
AM2R metroid 2
GZDoom, hello??
The Dark mod for Thief 1 & 2 in Doom 3
The black parade mod for Thief
Vampire bloodline actually making it playable. Same for KOTOR 2.
Without even going into the mods that became sensations like Counter-strike, Team fortress, DOTA, DayZ etc.
Shitting on modders is probably the lowest form of "look how edgy I am" I've ever seen on this forum.
It's downright stupidity or ignorance. Falcon BMS is something that can even surpass a multi thousand dollar game like DCS in its niche. You get a full fledge, almost "study level" F-16 simulator + a dynamic campaign simulator (something that developer abandoned) for ZERO.
Adding to your list,
These are the ones that i consider the right way to play many of these games. It surpasses the original product by a huge margin (or total conversion/completely different games):
Without even thinking too much:
MechWarrior: Living Legends
Roguetech - Battletech
Project Reality - Battlefield 2 and 3
Long War - Xcom 2
Stalker innumerous mods like Anomaly, Gamma, Lost Alpha etc.
Darth mod and innumerous others for Total War series
The game of thrones conversion for Crusader Kings 2-3
Movies Duel 2 - Jedi Academy
Yet Another MechLab - Mechwarrior 5
Antistasi, Altis life, RHS etc etc etc - Arma 3 (Arma community basically creates entire new GTA games just with a map editor and a bunch of LUA scripts. No wonder why Bohemia usually launch a game like Reforger just for the modders get ready for Arma 4)
GTA RP - GTA5
The entire Euro truck simulator community
Without even counting innumerous games that were born from mods (CS, Dota, DayZ, PUBG, Insurgency etc.) or mods that are the size, and better than, an official DLC (Fallskar, Elsweir, Beyond Skyrim etc)