Had an annoying day at work and going to get it out of my system here.

I've been told to delegate as many cases as I can to the frontline staff, but the review and handover process takes time. The frontline staff do not work at my level, so I can't hand them a case that hasn't been reviewed and expect them to be able to do what needs to be done. This isn't an indictment on them or me trying to big-note myself, the cases that I'm talking about are ones that have been sent to me by the frontline staff because they couldn't resolve them at their level. My job is to solve whatever the problem is and get them moving again. Recently we decided that I will hand cases back to the frontline staff with a solution rather than finishing them myself, because I'm only one person and there are a lot of cases. I inherited this role in February with a massive backlog and all the processes were inefficient and poorly-defined which is why it got so bad in the first place. It's not as simple as "Wow, now that we've made the decision that I will hand cases back instead of completing them myself, al
l this work is someone else's problem."; I still need to look at each case, determine next steps, prepare instructions for handover, and send them back. Today I was once again justifying the value of what I'm doing and explained that out of the 400-odd cases I started with, there are still 160 to go through the process. This review stuff is only a part of my job, I have a bunch of other things going on and I can't devote all my time to it. My manager tells me to pause all the other stuff and focus on getting all the remaining 160 cases reviewed and all delegable tasks handed over by lunchtime. It was quarter to 11. This is not even within the realm of possibility, but I decided to see how many I could do if I went full bottle. I ended up doing 87 by 4pm. Now 87 is a huge, huge number of case reviews to get done in 5 hours. I should feel proud but instead I feel sick from stress, because tomorrow I'm gonna have to explain that there are still 70-odd cases left, and I took 5 hours instead of 1 so nothing else 
got done and I'm behind on everything, and I'm pissed that nobody I report to understands what the hell I do despite having agreed on each step in meetings and demonstrating it for them multiple times. I wish I could give my managers 10 cases and double-dog dare them to get them done in half an hour.