Although you have taken good precautions against loss or theft of your laptop, you remain vulnerable to electronic attacks. In particular browser-based malware could take control of your computer and steal your PGP key.
The point of using subkeys is that you keep the master key somewhere really safe - which is not your everyday laptop. There have been other questionsother questions on here about where to keep your keys safe. A popular suggestion was to print out a QR code encoding of your key, and keep the printout safe.