Anecdotally, those 90% of users are not happy about their experience, they just tolerate it.
If you are forced to use an app with bad performance (say Teams) you cope. Humans are great at coping. Maybe you turn it off and back on again periodically, or alt tab to something else while it's showing a spinner.
It's true performance isn't a major selling point but IMO that's because most software products are not sold to users. They are packaged with other products, part of monopolies and imposed to users by others.
I buy video games where performance undoubtedly matters. Apart from that, most software I use, I didn't choose, and I'm pleasantly happy when it's not garbage (Outlook, IDEA) and annoyed when it is (Teams, Facebook). In either case, performance wasn't a contributor to my choice: I didn't have a choice.
All the sluggish steps led them to the usage of the web app they need to use, and they need it to be fast. At least, faster than rest of the crap so far. Heck, they may spend rest of the day with this app..
90% of the users use shitty hardware. Everything is sorta sluggish on their computers - they boot up slowly, the bunch of crapware in autorun take their sweet time to load & phone home, their wifi us overburdened with devices. Most of the software experience is sluggish for them. They don't care if their web app is sluggish too.