Pay no attention to the fact that I’m gay
He was forced out of his swamp, and discovered that the world had so much more for him to enjoy. He still goes back to his swamp at the end of the day, but with the understanding that he can leave and find other joys whenever he wants, which he does in subsequent movies. Fiona is the main reason he changed so much, yes, but he fell in love before knowing she was also an ogre. Even if she had been human, the story would be the same.
It’s basically the same as a guy living in a trashed apartment being forced by concerned friends to spend some time outside, and learning to live a more well-rounded life, while finding a partner with whom to share his type of lifestyle in the process.
You are insane if you believe that the story would be same without Fiona as Ogre. Shrek is unique and in this fantasy cartoon he finds easly: 1.A job 2. Friends 3. another unique female perfect fit for him. In real life the guy who lives in trash will easily die alone in a routine of meanless with hardly half of this listed things.
I’ve said this before, so check my post history for the full story, but I personally went from a guy who basically lived in a trashed apartment to someone put-together enough to attract the girl who eventually became my wife. All you need is the strength to say “fuck it” and try to better yourself in spite of your complete lack of faith that it will change anything. You’ve gotta get out of your swamp to find your Fiona. As for friends and a job, I’ve found that being more put-together helps with those endeavors as well.