I feel like this is also where dogfooding - or drinking your own champagne - comes in, if possible. We can use our software internally and sure, there are hard

I feel like this is also where dogfooding - or drinking your own champagne - comes in, if possible. We can use our software internally and sure, there are hardware costs and manpower overheads to run an additional instance of our software, but those aren't too high. Hardware necessary to run E2E tests of all the systems at proper scale including maintenance manpower probably eclipses those efforts. And then you'd have to add dev-hours on top of the E2E costs to build and maintain mountains of E2E tests. And this has exposed really nasty bugs in common paths already, just by employees using the system.