Before calling a worker slow, notice how often their work is interrupted.

Output gets judged as though the hours were whole. Someone who is asked three questions an hour is not doing the same job as someone left alone, because each interruption costs the work plus the climb back into it. The person who looks slow is often the person everyone else relies on, which is exactly why their day is in pieces.

Before judging, watch a couple of hours and count the interruptions, including your own. Ask what a protected morning would do for them and then arrange one. If that person is you, say how much of the day goes to answering others, since nobody can see it from outside.