I did a fellowship, and it was absolutely worth it. My area is not a natural fit for pharmacists, so it's unlikely that I would have ended up where I am any other way. There is, of course, a way to get there without a fellowship, but I would not have taken it - the time and the effort would have been better applied elsewhere.
It all comes down to what specifically you want to do in industry. Some departments are easier to get into without a fellowship with a PharmD and work experience (and residencies can be very useful) - medical information, medical communication, medical affairs, drug safety. Some are much harder, unless you also have another degree or work experience relevant to that field - health outcomes, epidemiology, marketing, market research, regulatory affairs. Fellowship is absolutely the quickest way to get to those positions.
Every pharmacist I have ever met in marketing, market research, business intelligence or strategy either did a fellowship or joined in the 'golden days' of 1990s or earlier. I have seen some people (with different degrees) transition from Medical to the Commercial side (and vice versa) but it's pretty uncommon. Overall, I would say, it's unusual to change roles completely once you get on a particular track. You may switch to a related role (med info to med affairs, MSL to in-house medical strategy, market research to marketing, etc.) but something dramatic like med info to marketing is rare. Used to be more common in the early 2000s but pretty rare nowadays.