I personally think "mobile first" should mean we force the devs to use a mobile device as their work computer until they all realize how fundamentally crippling mobile UI is and we all agree to stop shoving it on everyone.

It kinda does though, because modern software companies tend to shift focus away from projects before they get completely "done". The whole reason for "mobile first" is the tacit admission that whatever is not the primary focus will often get drastically less attention because there's already something that sorta "works".

There’s truth in what you’re saying, especially in the “things mostly suck, so expect that” world.

But in the ideal world you’re wrong... it’s fundamentally easier to start with a mobile design and make some specific interventions to make it work well on desktop than to do the opposite.

Whether anyone actually makes those interventions is, as you indicate, somewhat unlikely.

I've had to conclude that they think (or hope) that everybody not using a phone is using a tablet.

Yeah, but surely the vast vast majority of dropbox's business has to come from PCs. Given how hard (and wrongly) they are pushing to be a collaborative space for work documents, I think I must be correct about this. I know it's cool and all to imagine everyone working on their phones, I just can't see that as a viable work process atm.

but who uses the desktop web interface? don't dropbox users use the desktop app?

Some people use it by dropping files up to share with people, and don't use the syncing capabilities. It's a reasonably common use case, I've noticed.

Some people also use it like a USB dongle, and drop files up manually, then download them on computers they don't have installation privileges on.

I use it to sync the pictures and videos from my phone, which is then synced to my desktop at home, and then deleted from dropbox and thus also the phone. Automatically. If my phone gets stolen (or data deleted by some overzealous border patrol goon) it doesn't matter as much as it would have otherwise.

I do, because all the people at my office using the desktop app complain about bad syncs, sudden filling up of the local hard drive and general slowness

Sarcasm is hard. Unless I'm mistaken, you're imitating Blizzard and Diablo Immortal. If not then I think your comment comes across as extremely blind to a large segment of users.

I was forced to use web interface after app reinstall because Dropbox free account now supports only 3 linked devices (and I have 7).

Their loudest majority is probably mobile then.

Not necessarily a majority.