I have a T420, an x270, and have looked into modern ThinkPads like the P-series workstations, plus my current main computer is a System 76 Oryx Pro 9, so I can answer this a bit I think.

System76 laptops have [extremely good repairability for modern laptops](https://tech-docs.system76.com/models/oryp9/README.html) imho. Their legal terms and availability of parts, part info, and schematics make them much friendlier to repair than any other modern laptop, and they've explicitly and purposefully designed the laptops with swapping things in mind (think replacing the keyboard, speakers, cooling system, and screen, fairly easily). I'd say solidly superior to any new or recent ThinkPad, and even superior to my x270, but still not as good as my T420 of course — although it's the closest I've seen a non-Framework laptop come in potential at least.

They've also got superior upgradeability to my x270 (two RAM slots and two m.2 NVME SSD slots), but obviously it's nowhere near the insane levels of the T420, at least unless people start to leverage the easy swappability of the parts to replace them with newer parts instead of just replacing broken ones with new identical ones, at which point it might come closer. Reparability and upgradeability are two sides of the same coin after all.

Build quality wise, at least with my Oryx they're very much leaning toward "modern ultrabook" and not "military-certified tank", but they're built much sturdier than your average Lenovo or Dell ultrabook for my money. Probably even close to modern devolved ThinkPads! Not comparable to ThinkPad T420 or even x270 level though. Also be aware that the higher end models like mine (starting with Galago iirc?) get magnesium frames (magnesium being the same metal ThinkPad frames are/were made out of) and sturdier construction, whereas the lower end ones get plastic sandwich — nice plastic, but plastic all the same — unless you get the Pangolin (which I've heard also breaks the mold build quality wise and reaches near ThinkPad levels!)

As for hardware support, obviously you're going to get the latest and greatest consumer hardware, just hand picked for Linux and with (where necessary) custom drivers or firmware written, so you'll get equal to or better compatability than ThinkPads across the board — the crucial difference is just that you're getting brand new consumer hardware, instead of business professional hardware, which is often the same but a bit older and way overpriced (e.g. look at GPUs), so you can get a laptop for $2000 that'd cost $4000 for the equivalent ThinkPad P15 or whatever.

One thing to note is that System76 laptops have CoreBoot flashed instead of BIOS — again, with special core boot firmware written and sent upstream where necessary to support their hardware! — for more open firmware, and they also disable/strip the Intel IME whenever they can. They weren't able to do it for 12th gen Intel CPUs, but they were actually the first ones to figure it out for 13th gen. So if you care about having/supporting open firmware or are a cybersecurity hobbyist like me that hates the IME, that's something to consider.

All in all, I've had my Oryx as my daily driver for a bit over a year and 1/3 now and I'm extremely happy with it. It's by far my favorite computer I've ever owned. One of my friends recently, at my recommendation, bought a fully loaded System76 Lemur Pro and she's also very happy with it so far.