Proportionality of penalty for minor infractions; just cause for dismissal practice question

ABC Corporation employed Mr. Jose Santos as a regular Asset Auditor. On August 1, 2022, he and several co-workers were seen watching a movie on company equipment during office hours, despite being told by the Personnel Supervisor that it was no longer break time. The next day, Mr. Santos posted a sign on the office door stating 'No Urinating Here' without authorization, and when asked to remove it, he refused. He later claimed he posted the sign to protect a co-worker and that the video viewing was on the instruction of their supervisor to test the equipment. The company considered these acts violations of its rules on vandalism and misuse of company property, classified as grounds for dismissal, and terminated Mr. Santos after giving him notice and an opportunity to explain. Mr. Santos sued for illegal dismissal, arguing the infractions were minor and did not warrant the extreme penalty of dismissal. Should Mr. Santos' dismissal be upheld as valid? Explain.