Every time I download a mod adding followers or NPCs, my first action is to open up CK and tone down levels of the new NPCs and followers which are always overinflated, almost to the point it ruins the game atmosphere for me.

With all due respect to their efforts put into creating mods, why do modders always have to make demi-god followers who steal my character's thunder and mercenary/merchant NPCs who slay ancient dragons?

Some followers are even set as 'invincible', meaning they can't take any damages at all! I have no idea how adding bandit NPCs with 200+ levels can possibly conceived as lore-friendly.

I must the minority in this regard, but I always edit custom mods' content slightly worse than Vaniila contents so that custom items are slightly weaker(yet better looking) than vanilla items, and the same goes for followers and NPCs. I change custom follower's level cap to 30s and NPCs to 1~30 depending on their jobs and background. I value atmosphere over the game play, and to me level 30 + is a stage one can only achieve after hardships and adventures that PC went through to reach that level.

I wonder, is there anyone who feels a bit uncomfortable with level over inflation in custom mods? It's no big deal, as everyone has different taste and I can always use CK, but I still hope modders are a bit more concerned with lore and atmosphere when setting the power level of NPC or items.

Not all follower mods add invincible followers. If you have a problem then continue editing them or creating your own.

I go through every mod before installing it. I make sure it's structured properly and remove the parts I don't want. I sometimes modify mods to suit my particular playthrough in the CK, provided there is no other option. Be that another file or an in-game option, like within the MCM menu or otherwise.

It's not as uncommon as one might think.

Only used UFO and a few face replacers, never had any new follower mods, and it's worked fine for me mostly.