He played the role exactly the same as he plays nearly every role. The only difference between Picard and Xavier is the chair.
Whether that's true or not, it's not at all relevant to what we're talking about. You're changing the goal posts from making accomplishments generally to having a great deal of range or versatility as an actor. Going along with the red herring, though, don't necessarily judge an actor's capabilities on his typecast. Christopher Lloyd is an amazingly good actor, but anyone who hasn't seen his pre-Back-to-the-Future work, or some of his independent work, would hardly know it. Patrick Stewart was a successful theater actor prior to joining the crew of the Enterprise, including being a member of the Royal Shakespeare Company and acting on Broadway.
Regardless, though, it would be hard to argue that Keannu Reeves hasn't had any real-life accomplishments. But it would be equally hard to argue that he's a good actor. That example is only meant to illustrate the point, not to be a perfect analogy. The obvious big difference is that Patrick Stewart actually
is a good actor. He's very good.