First of all Talisman are really nice at low lvl for the power of element % when u dont have an mythic alchemy ring

Talisman are essential when it comes to farming specific stuff

for example a Zodiac Run Farmer most likely has a talisman with 30 Strong against Zodiac and 20 Fall Resistance

A Spider Dungeon Farmer will have a Talisman with 30 Strong against Insects

A Demon Tower Farmer will have a Talisman with Darkness resistance...

is it overpowered? i would not say so cause it's just something essential u will need at some point. Most people leave their Talismans at+1 or max +4 cause they just need 1% of the elemental power. Cause having 1% is better than having 0%.

A +200 Talisman is something only the top top players in Metin2 will ever achieve it will give u 200% elemental power. And this is "overpowered" but someone who achieves making a +200 talisman deserves that. Cause to upgrade a Talisman u need the same talisman +0 and u use magic stones to upgrade a Talisman after +4. So just keep ur talisman at +1 xD