It is inevitable for Geralt to become "super-witcher", it does not matter really are you doing main or side quests, or contracts.
About side quests, some of them will fail(that are connected with main story) but most of them will be available after completing main quest. As for gwent, I dont...
Ciri is not true witcher, she did learn some basic witcher swordplay, but she is not witcher. And maybe even more important, in whole book series, as far I remember, only monster she killed was that young wyvern in Gors Velen.
I cannot believe what am I reading. OP is complaining because there are enemies with bigger levels. It is completely normal that when you start game, you cannot beat everyone. There are zones where you need to level up before you can beat enemy. If this werent like this, you could go basicly...