yes, it's the amount of mods. No matter the mod type, it will use more CPU as it is usually adding something into the game not already there, meaning the game gets bigger. Also, the "Sweet Spot" would be based off an individual PC hardware, and even the software (ie, if you don't update often/at all due to it causing issues/disliking the changes) though not nearly as much if at all enough to notice unless you are incredibly behind on updates. I will say that over 100 mods will cause most PC's to skyrocket in temp. You'd need some of the newest stuff to do something like that and not have a decent increase in temp. Believe it or not, a lot of cosmetic mods don't add as much as you'd think if it's replacing units already in the game, as it just switches out textures for a new one, so there is slightly less of an increase to data there really. Ones adding completely new stuff, like weather effects or extra particles and even Magic colors if it's just added onto what is already there will do so normally as it's "new data" (Magic color ones would depend on whether it completely replaces a texture with a new one, which would actually cause less strain even if the data change is the same as one that add more textures to magic spells as it only needs to find one file, not two.) But overall over 100 mods WILL cause your PC to heat up more than usual as it is having to deal with much more data than before. Mods add new data, or change what data is there already. Most of the cheat ones change what's already there to different numbers. (Still slightly more to process, but no more than what's already "possible" to happen without said changes, as even with buffs to units, those already exist as numbers in game, it's just set to 0 until you get techs or lord skills.) Some might add things, as you could consider adding more slots for buildings in settlements as a cheat.
Mods that add things will of course be ones that add new Units, Spells, Lord Skills, Lords, Heroes, Factions, Items etc etc; Weather ones too if the textures and animations for said weather was not in the game before, for instance, if it snowed on battle maps that didn't show snowfall before. it 's copy pasting whats used on other maps and putting them in those maps, meaning it's adding more data. Of course some mods might just completely replace them with their own animations and textures, which might be bigger or smaller in size.


Over all, yes it's the 100+ mods you have. Take it down a notch. I'd say half a it to 50, than 25 if it's still getting hot, and than remove like 1-2 mods at a time or something till it gets to a temp you want it at. Even if it's just your graphics card that gets hot, it's still having to deal with at least some of those mods as I'm willing to bet that some of your mods add units yes? That's new Graphical data that wasn't there before, whether it's being shown on YOUR screen or not, it's somewhere on the campaign map, meaning it's at least partially rendering it so it isn't causing a large sudden load once it comes into view out of the fog of war. Battles will also cause it to heat up more as new units will be more data for it to sift through and find images, textures and animations for.