But later we see that Sho was able to do much wonders with the Guyver I unit and at many times we see that the unit itself made the user almost immortal.

During a battle with Archanfel, He was blown into bits and only the Control Metal remained, which fused with the control metal of the Creator's ship. This happened because he suddenyly was filled with only the desire to become stronger to protect his friend from harm. Unlike Agito whos desire was to conquer. This sense of longing was much stronger than greed amd the Creator's ship gave him that wish.

However, because Sho was mentally weaker than Agito, he lost the Gigantic Armor to Guyver III... ... But from the later series, we see that the Guyver Unit alone was very powerful by itself if the welder desired to be stronger as he destroyed a whole horde of Zoanoids and took on the mind controled Aptom. This shows us that the Gigantic is only a boost to RAW power but if the user's mind is still weak, he will not be able to use it properly.

Sho has a strong sense of friendship which guides him to protect his friends from harm.

My Comments
A typical loser turned "forced" hero. Inside Sho just want to go back to where they was again but is fighting only because he wants to protect those that he holds dear to.
He is not weak but just unable to make up his mind on where he stands. If one day, Sho's fighting instinct is awaken his powers may even over take that of Guyver III