During the pandemic, my daily drop average trebled from 55-60 drops per day to 180 per day, and since things have opened up it's still double what it used to be on an average day of about 120 drop, like you say, a workload that was forecast 5 years from now. In a city that's easy and they come off quickly, but on a rural route like mine, I'm covering 200 miles per day and 5 postcode areas, mainly on country lanes and forest tracks for some deliveries, still working within an hour time slot.
I'm actually a joiner by trade but had a complete change just over 3 years ago to become a courier. I chose the wrong time, that's for sure. The money during the pandemic was worth it, but we were working for it too, the lead up to Xmas when folk were in lockdown was sometimes 16 hour days. It's certainly not the easy cushy job people thinks it is, I was shocked when I changed career just how much work it is, but I love it. Not only has it got me out of a dead end 22 year career, the mental aspect of the job has benefitted me greatly to the point my social anxiety has all but disappeared over the last 2 years because every day I have to speak to people I don't know or go into places I don't know, that has always been one of my major anxiety triggers.
Sorry for the slight tangent!
