Thanks to your comments, I was able to reread this again. I understand you have to pinpoint the only time he said something cruel which is valid BUT CAN YOU EVEN NAME A MORE GREEN FLAG ALPHA than him??
-Never assaulted MC despite they are in omega verse and MC got amnesia.
- Treated him with respect and PRECIOUSLY!
- Loves him more than he loves himself.
Also, stop pretending that Ren don't have his own personal BAGGAGE like Yuu. He literally grow up with inferior complex and thought he was a defect despite being an alpha all his life. That's literally why he's more compassionate and empathetic more than everyone else, that's why he thought he's not fitting for Yuu. I felt like the ending, with Yuu pursuing him after realizing the things he have done from him from other people is the best ending. They are the best pair.
I can't name a more GREEN FLAG ALPHA THAN REN!! They are match made in heaven. I hope they show their babies.