We can't seem to decide if we want them to replace all of our devices or only a few of them.
No, 'we' haven't shown any confusion on the matter.
The tablet fills the niche of folks who needed 'good enough' compute power in a no-muss, low weight form factor. Analysts and tech media got caught up in the adoption rate by the large untapped market and assumed such a huge surge in sales *surely* meant it was going to supersede personal computers.
Fast forward to today, tablet sales have flatlined because the 'good enough' market has gotten their devices and there's not much of a drive to upgrade constantly. Phones got a bit of a boost by manipulative service plans 'subsidizing' the cost of a phone every two years, but now that's faltering as carriers move away from that, as people *mostly* weren't upgrading for latest and greatest function, but because they were getting one 'for free' every couple of years and 'hey why not' in that scenario.
Meanwhile PC sales have certainly faltered, but not as severely. That market is still driven to some extent by upgrades, at least moreso than the tablet market.
Note that this is bad news for hardware makers and suggests large investments won't pay off in that space, but it does not mean a software developer should ignore the install base.
Personally, I have a desktop, a 12" windows tablet (lenovo x1 tablet) and a 10" android tablet (yoga tab 3 pro). My desktop is for games that can make use of the high wattage components. My windows tablet is basically general laptop usage, with the option to occasionally rip off the keyboard. My android tablet is the best for reading various media (in part because there is a lack of touch friendly windows applications for reading, in part because the hardware form factor with the smaller screen and the bigger battery oriented in a convient way make it better for holding to read).