I do not believe roles should always be adhered to, or rigid in executional aspects. Especially given that seasoned designers have learned a great deal more about design and have the ability to overalp, negating the need for other positions.
A model should be defined and built around the team itself, and the objectives that need to be met in order for the work to be a success.
There are a lot of hybrids these days, both as fulltime employees and contractors. And clients don't know how and unfortunately, some managers couldn't effectively evaluate process and structure without someone having already defined one for them. Which is to say, when it's new, there is nothing to gauge it by. Be willing to be new. It's what clients are paying for.

Roles typically depend on the size of the project, the amount of people that need to approve it, and how marginalized a team's abilities are in an effort to create a factory assembly line for design. There is a belief that a designer is simply a hand, while 10 people are the head. This is destructive, and usually hinders, if not squashes, new design patterns and techniques. A designer is a problem solver, first and foremost. If the information used to inform the design is constantly changing, then the design should be re-evaluated in contrast with the new information. Put another way, personal opinions have no place in the design process, and arbitrary comments guide nothing.

I highly respect the roles people play, but I appreciate when they're given the ability to look at and participate in other aspects of the same problem. Ideas and solutions can come from anyone, but it's usually one or two wrists who become responsible for creating it, and in some cases, fixing it. Once there is actually something tangible to look at; the real thinking begins. Stick to the facts and information, try not to infer or inject personal tastes into your branding and marketing.