I think we have a fundamentally different view on this, your interpretation is that if Mc transforms himself in a material resistant to electricity he wouldn't be damaged/as damaged. Mine however is that it doesn't really matter what material he transforms into, if it comes in contact with electricity it explodes.
Yeah, obviously we have different opinions.
I think the main problem is that we both understand differently the properties of his transformation.
The way I see it, your point is that regardless of the form the MC takes, whatever he creates is still de facto part of him and therefore subject to the same rules and weaknesses as the rest of his body. So if MC's Weakness was water, for example, it wouldn't matter if he created a completely water-resistant and waterproof surface on his body, it would still hurt him immensely if someone splashed him with water. (Please correct me if I misunderstood you.)
MY opinion is that the material that MC creates really has the properties of the given material.
Waterproof material will be waterproof and non-conductive material will be non-conductive.
The reason why he has problems defending himself against electricity is that there aren't exactly many organic materials that could provide him with resistance to it. Amber was literally the only material I could come up with. And even that is more plant-based than animal-based.
Anyway, I understand why you think it is the way you think. His transformations require a certain level of concentration. Even if he had partial protection against electricity, the moment the electricity gets through, his entire defense will fall apart, as he can no longer maintain that protective form. This is the part where I agree with you. But if the electricity doesn't get through at all, I believe that the MC will not be damaged in any way. So he really needs 100% protection, because for example 95% protection wouldn't be much better than 0% protection. Once the electricity gets in, everything starts to fall apart.
P.S.
It's not like everything the MC creates is necessarily a fixed part of his body.
He was able to shoot bone projectiles during battle and if I remember correctly, he once told the girls that he can cum inside as much as he wants, because all the parts he separates from his body will evaporate within a few minutes (and he was MUCH weaker then than now). So if he learned to create amber, technically there would be nothing stopping him from creating amber armor, or a shield, separate from his main body. Even if there was still a limit of a few minutes, I don't think he would need them to exist much longer. Actually, it might be enough if they could only withstand one or two hits, because seeing how quickly he was able to regenerate his destroyed body, a few dozen shields are nothing.