There are a lot of problems with having purely generalist positioning.
The main one, though, is that potential clients don't know what you're actually good at.
So they're left to figure that out for themselves—and there's no way to tell what you're actually good at until they work with you.
And by then it's too late.
The best clients will go to someone who looks the most qualified on paper. They will spend top dollar with them to do things right.
And that means you'll be left with the less-than-ideal clients. The ones who don't understand just how nuanced the work is to do right—which means they won't value your work enough to pay you well.
They'll be price shopping and have unrealistic expectations based on naive perceptions that things are easy.
Yes, I think you can be a generalist and specialist at the same time. You can build around your best skills and ideal niche until you don't need to take on other clients.
But having purely generalist positioning is a recipe for having a business you don't want to run.