Well, fellow posters, think about it. How many "mainstreamers" linger or even look for this site and forums? Most of the folks coming in here build their own desktops and servers.
So we have a bias about this issue -- Lenovo, Dell, HP . . .[several others including the boutique systems] -- versus -- choosing the parts and designing your own system.
I have all the time in the world, and I choose to devote a lot of it to this pastime. I may take a year concocting a general plan for a system, by which time the CPU and chipset choices may be superseded by the new releases.
It's actually easier to embrace the parts-match process if you tend to favor high-end or second-tier to high-end systems. The extreme of that are the Intel "E" processors using chipsets like X79 and X99. Second tier would be the 4-core enthusiast CPU "K" processors with unlocked multipliers. If that makes it easier, the budgeting and "cost control" is still harder.
There was a time during the 1990s when I was sure I saved money building systems on my own, but that has changed a bit. I always spend more now on a system than any mainstreamer looking for a desktop or even a gaming rig, excepting those with the ducats to buy a high-end boutique system with water-cooling all put together, overclocked and tested.
So these days, I don't build my systems with the sole imperative of saving money, and I know I'm going to spend more.
But I've serviced enough OEM systems and poked around inside them that I can say I wouldn't be happy with one. Yet -- I've harvested parts from them, like drive cages.
So I would at least look at my usage pattern and the software I use, and make sure an OEM system was capable of fulfilling those needs. that is, I would take that approach if I didn't incline to build them myself.