Have you ever encountered traversing a long list of students on speed grader back and forth? Perhaps you want to grade a specific student and you have to scroll to find the name?
The current practice in our university is that all same courses under one professor, regardless of number of sections, will be grouped in one canvas classroom. The main idea behind this practice is to ease the job of teachers in posting assessments, instructional materials, etc. as they have to post in one canvas classroom only.
Hence, if you have 40 students per class and you have 3 sections of "Software Engineering", then you have 120 students on speed grader of that canvas classroom. I know it's not a problem when you are going to grade their activities from top to bottom, or vice versa. Or if you will filter it according to their respective sections.
Still, I think it will save a lot of time if you could just have a search engine within the drop down menu. It's actually easy to achieve in coding. See the searchable down menu in action: https://select2.org/dropdown