There must be a Product  Owner,  a Dev Ops lead,  a UX designer etc.  Yes these activities all need to be covered, but when you start  giving people roles, it creates  a desire  within people to fulfil  their role at all cost - dangerous stuff.  Thinking back  on all the dev teams (including Agile, RAD, Waterfall) that I've worked with, the best ones included at least  one  of each  of these  types.

The Creative

Bringing  great ideas to the team  and  to the business.  This is  not  always  the official 'creative'  on the team.

The Cynic.

Points out all the flaws in the Creative's bright ideas. 

The Pragmatist

Finds a way  to deliver great ideas  that  work.

The  Implementor

Just  gets on with it  and  saves the  team from  disasters

The Destroyer

Every team needs someone that has the knack of breaking things. They can come up with unhappy paths that no-one ever dreamed of!  Sometimes they are called testers, although  not all testers have this  ability ;-)

I hope that  gets you thinking about your  team and how it works.  If  you have any thoughts on  this theme  I'd love to hear from you. Who  knows, I might  be able to  gather enough data to prove I'm right!