Effective teams do not need clearly defined roles. They need clearly defined goals.
The goal gives rise to needs and the team self organises matching members to needs.

If you have to impose a structure on a team externally, either it's not a team, or you were just describing a traditional grouping of employees as a team in order to look modern and progressive twenty years ago. So in the latter case, never wanted a team in the first place, at a wild guess what was required was a manning reduction.

An effective team is self managing (which is why real ones are massively unpopular in corporateville), now if you want to help with that fine, If you want to manage it and you aren't a member, jog on....