They are all different and complementary products. Like most, I have a desktop, a laptop, a tablet, and a smartphone (ok, more than just one in each category and I am not including servers, SBCs, etc). Like most, I have considered trimming down to 2 or 3 devices but I have never felt comfortable enough with any of the combinations.
There is no way ANY laptop (let alone tablet and smartphone) can replace my desktop/workstation. I need a separate keyboard, I need a mouse, I need multiple large screens, I need expandability, I need upgradeability, I need maintainability, I need CPU/GPU power, I need storage and network throughput that exceeds the capabilities of laptops. And even though Desktop OSes and Desktop apps have been regressing into mimicking mobile-like UIs in this era (ugly UIs designed by youngsters or targeting youngsters or non-tech-savvy users) they are still better than what I can get in Android and iOS world.
Since I mostly use a laptop for bringing and continuing work from home to workplace, give a presentation, etc I played with the idea of replacing my old i9 MacBook Pro with my iPad Pro. It never worked. It was never easy to type, select, search, move, scroll in iOS, it was never efficient to use a mouse, it was never easy to connect to old Video Projectors, it was a PITA to live without analog audio output. There were many situations where I needed Ethernet instead of WiFi, times where I needed data exchange using physical storage instead of the cloud. I found myself carrying multiple dongles and being frustrated every day with both the hardware and the software.
At home, I NEVER use a laptop. If I am not computing sitting at my desk using my desktop then I will be using an iPad on the couch for checking (not writing) messages, videos, reading/annotating PDFs with the Apple pencil, maybe even a bit of Web browsing (IF it is about simple things and doesn't require typing, opening tabs in the background, finding text, etc). I also use the iPad if I want to browse=search=discover music albums, composers, artists, genres, etc on Spotify, Audirvana, or LyrionMusicServer and play it through my audio streamer. If I only need to pick a playlist and start playing it then I am fine with a smartphone and the corresponding apps. For video & movies on Plex I am ok with just using my AppleTV.
I have entertained the idea of replacing my smartphone with a standalone smartwatch (i.e. mainly used for phone calls and checking messages) plus an iPad Mini (whenever it is possible to carry a bag). I'd rather wear my old Casio any day, it doesn't need to be charged daily, a beeping alarm is all I need from an alarm, I only miss the smartphone, I don't really care about photos. Sometimes less is more, I find myself wasting hours and hours looking on my smartphone, waiting for an email or SMS, reading silly news and videos, playing silly games, etc, and I do not even do social networks (LinkedIn doesn't count). I feel addicted to Internet and there is no easy way out.
If I am on the go (bus/train/flight) then it is most certain that I will be carrying a bag - I can always listen to music and watch movies on the iPad I am carrying. But it will be a struggle if I need to operate on one hand, translate, etc - the smartphone is mandatory there. If driving, then I am not sure if it would be possible to replace a smartphone with a smartwatch for Google Auto or Apple CarPlay. ONE thing that has helped reducing the clutter is having a single USB-C charger for everything (thank you EU).
Eventually, I have resigned to the idea that I will never be able to reduce the number of devices I use daily without getting frustrated. Still, it would be 10x worse if the industry keeps consolidating and dumbing down software and UI. One size doesn't fit all.