One reason why so many developers have "power horse mobile workstation", is because that's whats handed out by employers. Desktop PCs for devs, management, etc. are a rarity in the office.
As to the question, it depends on your needs. If you do most work at home, and have the device powered on most of the time anyway, then yes, a beefy desktop machine paired with a relatively cheap (as in "not a big deal if accidentially destroyed by bad luck"-cheap) is a good idea.
I upgraded to an Asus Zephyrus G14 (2021 edition) at the end of last year, as my T470s was getting a bit slow. The dimensions are smaller than the Thinkpad, but it weighs slightly more (1.7kg).
The thing is though this is a gaming laptop... under the hood it has a Ryzen 9 5900HS (8c/16t), 32GB RAM and a Nvidia RTX 3060. It runs the test suite more than twice as fast as the Thinkpad it replaced :D
When using the integrated graphics and with performance set to quiet the fans rarely spin up. It gets around 10 hours battery life. No issues with Linux. My only complaints are that it has issues with USB PD charging and the power brick is a bit big, and there is no webcam (fixed in the next gen version)...
I have something like your idea. My previous desktop-ish-equivalent laptop is now my kids-gaming, A/V & travel (uh, when we can do that again) machine. My desktop is a very nice ThinkStation.
My employer has provided an astounding Dell Precision laptop which sits on my desk at home or at the office during the week. Weekends and evenings it's away.
I definitely appreciate that my desktop does not get over 80°C no matter what I do while the work laptop easily reaches 100° when it gets busy.
It's very good for my mental health to only 'compute' at a desk.
I think a desktop offers more than a laptop if you use it stationary, although I think the difference is smaller if you want to stay on MacOS.
Most developers I know have both, desktop and notebook, which both are powerful. If you are an employee, let yourself get treated a bit, but even if you want to buy it yourself I think two devices have an advantage.
"Given the current trend of MPB's with huge specs and associated huge cost, it seems foolish to me that we as developers spend that much money on what is basically a desktop machine. A machine that makes compromises due to thermals and power efficiency while actually being a desktop machine."
This only applies if you never/rarely actually use your laptop for mobile purposes. While I have a monitor and desk setup that my laptop is plugged into, I travel enough or work away from my desk enough times a year that having a laptop makes sense. I prefer having one machine over having a powerful desktop and a cheap laptop. Ultimately everyone have different preferences for how they work. You should do what works best for you.
I'm laptop all the way, because I do tend to move around (even with Cövïd and mostly staying home I still enjoy moving between rooms, or out on the terrace). Maintaining both a good desktop and a good laptop would be a) a cost issue and b) an adjustment issue (or at a minimum, a sync issue).
If I were in your situation I'd definitely go for desktop only, which has obvious advantages like easy upgrades and price.
> Given the current trend of MPB's with huge specs and associated huge cost
I'm on a Air M1 and have a really hard time agreeing with the "huge associated costs". It has moderate cost (compared to whatever ultrabook), combined with huge specs (in comparison).
Eh I am of similar mind. Overpowered (for my needs) desktop and I just picked up a Asus vivobook flip with a AMD 5700u for mobile work. Desktop and laptop in the last 6 months has been my first hardware upgrades in about 6 years.
I have been using a desktop system with three LCDs and a mechanical keyboard with trackball for over five years. My mobile system is a Samsung ChromeBook.
The best thing about the desktop is that I can easily upgrade, replace parts as the need arises. I have a small UPS so that power glitches don't cause crashes. The best part is the entire desktop configuration cost less than a highly spec'd MBP.
When I'm on the road, the ChromeBook runs all day long, so I don't need to take a power brick with me. It's like having a MBA at 1/3 the cost.
For me, my biggest concern is for fan noise. if I'm working on Windows, I prefer desktop, as I hate the fan noise from the laptops. Desktops also have lots of options in peripherals and upgradeability, especially in CPU and GPU.
If I'm working on MacOS, I don't have any preference as long as it's M1 based, since they run silent in either as laptop or as desktop.
I like one thing about laptops, if there is a power outage you will not lose all of your work. Yes, you could buy UPS for computer but the fact that laptops have batteries is the main reason why for past several years they are my main computers.
I prefer a touchpad to a mouse...and the laptop's touchpad is convenient to the keyboard so it is even better ergonomically (for me at least).
Like others have said, work provides me a laptop that's sufficient for the job. I probably wouldn't buy something like that for myself.
For personal use, it is basically your current idea. I tend to have a reasonably powerful desktop and a fairly inexpensive laptop. Powerful desktop parts are cheaper than powerful laptop parts. They're easier to upgrade. They're easier to fix when something dies.
If I need more than my laptop provides, I use the desktop. Sometimes I sit at the desk. Sometimes I remote into it. VPN and wake on LAN means I don't even need to leave it on.
This also means if one device dies you're still able to get things done. Laptop is slow, but better than 0. Desktop is not portable, but I'm usually home anyway.