I worked for Follett for over 30 years in a variety of rolls from Sales to Management. One of my strengths was operational efficiencies. A core tenant that always served me well was a management concept "If you don't measure it, you can't manage it!" A common theme I see in the comments here comes down to time. So here's my question. Have you ever measured your actual time spent? If not, I highly recommend you do so. You will learn a great deal. You'll discover spending more time doing some tasks than you should. You'll discover some tasks that you should stop doing and others you should start. You'll ask, "Why does this take me this long?", and make changes based on that. Most importantly, you'll have hard data for that discussion with leadership about how overloaded you are, if you find you truly are. It's a much more productive discussion when it contains more than generalized claims. I justified headcount increases during hiring freezes at Follett using hard data driven impact and revenue analysis based on time measurement.
A tool I can suggest is called Toggl Track. (https://toggl.com/track/) You can use an account for up to five users for free. There is a little time involved to set up your tasks and it does take some discipline to get in the habit of logging time. Once it's set up, it does not take much time to log time. It's nice that there is a partner phone app tied to your account so time entries can be easily done as you are on the go moving from task to task.
Remember... "If you don't measure it, you can't manage it!" If you want to make a case to management? Have some hard data. I hope someone finds this helpful.