I'm not sure if this forum still lives, but I'll try posting here, since I didn't find an up-to-date answer.

Does level of your follower matter? Does it matter if you have follower that is level 50 and you already 70?

My concern is, that I really love Serana as my follower, but I discovered on wiki that she stops on level 50, which kinda disappoints me. She is still able to solo a groups of enemies and hardly lose any life, but I'm afraid that enemies will become harder for her to deal with.

I don't really want to change her for someone like Frea with no level cap, but I don't want my Serana to start chain dying either. She also feels less valuable.

So, should I change her for someone with no lvl cap or just don't mind it?

Btw, does anybody know if there's a simple mod (I don't want any of those full follower overhauls mods) that would allow me to level my Serana further?

Eh. Doesn't really matter. You can still drag the yappy undead [censored] around with you. Try to avoid the higher level dragons, though.

If you are going to rely on the follower for more then pack mule purposes then yes the follower's level does matter. As they level they will have more health, stamina, magic pool. stronger weapons skills. So yeah, I say it does matter depending on how you use em.

UFO (Ultimate Follower Overhaul) is simple enough to use. Lets you take multiple followers, control what they wear and use in combat. AND it removes the lv cap as well as essential and non essential follower tags if you like.

Level 50 is pretty high for a follower, so I wouldn’t mind it unless you actually notice a problem with her taking a knee all of the time. If you don’t want to use a mod you might look into increasing her maximum level or attributes with the console. There’s a uesp page that lists and explains them. Look under Targeted Commands. Of course be careful and save before you do in case something goes awry.

Other than a few dragons, and some DLC enemies, none of the enemies in the game go above level 50, so Serana will be fine.