Well my main and newest PC is a Thinkpad W541, it is 11 years old. It is plenty powerful and I expect it to be useful for at least another 10 years. All I did was replace the HDD with a SDD a few years ago.
There is no real reason to buy a New Laptop these days and to me, many people buy new just to get the latest OS from Microsoft or Apple. They claim "slowdown" is the issue for buying new, but mostly it is cruft those Operating Systems builds up over time.
With Linux or a BSD, you will see how a real OS is suppose to run.
If you do buy new, make sure it is user upgradeable. For example, memory is not soldered onto the board, hard disk (HDD/SDD) can be replaced.
This must be use-case dependent. I don't use laptops very much, but I still have the parts from my PC from 12 years ago, and I remember the difference from when I upgraded 6-ish years ago. The difference in the CPU alone was significant, not including the GPU and RAM. I expect to see similar improvements on my next upgrade. I don't see why that wouldn't also apply to laptops.
Though, the average person is probably getting significant slowdown from accumulating background applications.
For the machine I do web browsing from it can be anything, same with my D&D character sheets, anything, right now it is my phone.
But my games need a high end GPU and that scales with time. My workstation needs to build large C++ projects and I will never have enough cores or RAM for that. I am getting a threadripper with 196gb of RAM and the only reason I didn't get more was price. I will use it all, and a hearty amount of swap space.
If someone it just SSHing into things to administer them they don't need more. If some is gaming they always need more.
Actually I forgot this case, GPU may be the only reason to upgrade when the person is using heavy graphics games or maybe autocad or 3d modeling type software.
But if you ask me, these people may be better served with a desktop where you can upgrade the GPU Board every so often.
I feel like a 11 year old ThinkPad would be pretty slow at modern web apps like Gmail, especially if you have a lot of tabs open.
My 7 1/2 year old ThinkPad was painfully slow loading Gmail this morning for some reason though the fault could be 100% on Google's end.
My Thinkpad is also noticeable slower than a high end modern desktop running Windows at doing simple things like browsing for files, though that doesn't discount the possibility that it's the OS's fault.
I feel exactly the same way. My main machine is an 11 year old IdeaPad with a 4th Gen i7, 16GB of RAM, and an SSD. No performance issues whatsoever on Mint. From what I recall, battery life isn't great, but I've used it exclusively as a desktop for most of its lifetime.
Windows on the original 5.4k disk, especially booting, was a truly awful experience.
My "lounging around" machine is a 14yr old Dell E6510 with a 1st gen i5, 8GB of RAM, and an SSD. It also works like a charm with Mint.
There is no real reason to buy a New Laptop these days and to me, many people buy new just to get the latest OS from Microsoft or Apple. They claim "slowdown" is the issue for buying new, but mostly it is cruft those Operating Systems builds up over time.
With Linux or a BSD, you will see how a real OS is suppose to run.
If you do buy new, make sure it is user upgradeable. For example, memory is not soldered onto the board, hard disk (HDD/SDD) can be replaced.