Please find below my experience details:
-Separation of concern
-Easily understandable by developer becz it's standard practice, and reduce KT time.
-Code quality because developer with Helix knowledge knowing it where to add which solution/file/classes when process streamlined
-Re-usable. Lift and Shift
-Agreed with you. It will increase build time which affect CI/CD pipeline
- Helps in Sitecore support