What is the point of mystic?

You are not meant to just shoehorn it into an unrelated build that does not already use one of the champions.. that is not how TFT works for mystics or anything else.

So you are saying only a light-blademaster combo suppose to have magic resist? Shouldn't an important trait like MR be available for evey comp who wants to counter mages in lategame? Not to mention how viable a light-blademaster combo in the current meta. You have certainly no issues with mages in late game with it since you will never get to late game with it. Anyway, it is not like the light or the blademaster trait has anything to do with the mystic trait. Do they amplify it to be more effective? No. You take the exact same damage from mages like any other comp with mystic. Therefore, your argument doesn't make sense.

And yes, it definitely does do something. Again, inarguable basic fucking math. Just because you cant does not mean it is a mystery.

Since you are clearly unable to comprehend my issue with mystic I give you an easy exampe: let's say a mage deals 1575 damage *2 (mage comp) = 3150 dmg. Champions have 20 base MR so my champion will take 2625 dmg and dies. If I build mystic which is +40 MR my champion takes 1969 damage so still dies. 1800 - 2625 < 0 and 1800 - 1969 < 0, it is "inarguable basic fucking math. Just because you cant does not mean it is a mystery." Then I haven't even mentioned the fact that mages build Seraph's and they have ocean trait (they can build crit for spells too), so they can machine gun you with shots like this. Even if a tankier champion has more hp still dies a in few seconds later.

All in all, your champion gets oneshot with or without mystic. If it makes you feel better when you can tell "I got oneshot and lost the game but I mitigated more damage!!!" then keep it up, have fun with it. I am more practical and trying to win while having fun.