We're probably going to agree to disagree based on definition, but objectively, he took 16% of the team's shots when he was on the court and had a usage rate less than 15%, 6th and 7th on the team, respectively. KenPom defines roles based on usage, and has that <15% usage in the "limited role" category, which is actually one category below offensive role player. There's 5 guys on the court and he took shots/used possessions 1/6 of the time.
He had a very defined role: floor spacer/3 point shooter and 3/4 wing defender and supplemental rebounder and very rarely did anything outside of that role. He was a pretty classic 3&D guy, which is one of the most well known role player roles.
He was very effective in that role. In fact, he's still a role player on the German national team, and the reason he is still being selected for the team at age 30 is because he knows and excels in said role.