I dunno how difficult this would be to do but currently those potion effects only affect the player, meaning that these do nothing to the mob itself if they're affected by these effects.
An Arrow shot by a Skeleton that's inflicted with Archery/Klutz could have it's arrow damage increased or decreased depending on what potion they have.
A Guardian's eye beam could have an increase/decrease if inflicted with Magic Focus/Magic Inhibition... if the eye beam is actually affected by those potions. This also includes it's passive "thorns" effect which IS actually affected by Magic Focus/Magic Inhibition... but only for the player currently.
Note: Guardians actually hit you twice in one tick, one for a melee hit and one for it's "indirectMagic" hit. Only the melee hit gets a buff/debuff from Strength/Weakness Potion effects. This was found out by using ToroHUD as it'll show you individual damage pop-offs and you should see two 5 hit splats if the guardian lacks any buffs and attacks you, as shown in the image below.

ToroHUD has a bit of a thing for showing rounded up damage but if you look at my health bar, I took 9 total damage from that guardian.