I don't think this is true (that if you purchase Delta Comfort Plus, you will board before Main and Economy so won't have an issue getting the overhead bin space which is allegedly dedicated for your type of ticket.)
Here is the list of Delta boarding groups up to and including Comfort Plus. So if you book Comfort Plus, these people are getting on ahead of you:
Pre-Boarding
- customers needing assistance or additional time to board
- active Duty U.S. military with ID
- Delta 360 members
Zone 1
- Delta One customers
- Delta First Class Customers
Zone 2
- Diamond Medallion Members
- Delta Premium Select customers
- Early access for customers traveling with car seats and strollers
Zone 3
- Delta Comfort Plus customers
(I'm not including zones 4-8)
https://www.delta.com/us/en/check-in-security/boarding-priority
Also
https://thepointsguy.com/news/delta-air-lines-new-boarding-groups/