It's a slightly better result if you change the conditions of the matchup. You've resorted to a gray area market (similar to Kinguin) with the repurchased Windows keys. Additionally, you've ditched wireless connectivity, nerfed the B360 motherboard standard where an actual motherboard sample taken from one of these units-- the MSI Bazooka-- was used, nerfed the faster HDD, and arbitrarily decided that a more expensive "pretty" case isn't desirable.
Again, we've done this before. You cut corners to make up ground in cost when I'm just attempting to demonstrate that one a component-to-component basis the AIO market is delivering the same hardware for less money. I'm not presenting the absolute best value the AIO market can offer. I'm just referencing the #1 bestselling gaming-class model that also happens to meet the most popular current mainstream gaming hardware profile on Steam for dedicated PC gaming. Things get more complicated, yes, I agree, if we start probing where each strategy is more viable against market competitors.
For example, I could choose the Amazon #1 bestselling Tower unit of all, the refurbished
HP Elite 8300 SFF for $195 (i5-3470 + 8GB DDR3 RAM + 500GB HDD + DVD-RW + Win10 Pro), and marry it to a 75W TDP low-profile Zotac GTX 1050 ($150) or 1050 Ti ($200) which can comfortably piggyback on the 300W PSU via the motherboard as well as fit in the case. For $345-$395 you have viable gaming power for a purchase path that's most complicated task is seating a card in a slot, and RAM can also be expanded cheaply-- for the moment.
The GTX 1050 Ti 4GB scores an 8.7 while the GTX 1050 2GB scores an 8.1 on Game Debate for the 1080p resolution. The i5-3470 notches a Quad Core Mixed score on UserBenchmark equal to the Ryzen 3 1200, i3-7350K, and significantly beyond any of the Coffee Lake "Gold" Pentiums. It's going to be nearly impossible on the self-building market to crack that
$345 floor. That's on par with Console gaming prices ($180-$485), and the Ti version is considerably more powerful than the Xbox One S or original PS4. This is a processing core that can be expected to average above 60fps on
Overwatch@1080p at High settings (GTX 1050 Ti avg <85fps) so this option can handle any eSport-class title. Guys who are interested in PC gaming at the bare minimum would find this highly attractive.
HP Elite 8300 Small Form Factor
This strategy can be pursued with SSDs, too, although it's much less effective for higher-performance builds since AIO PSUs tend to be crappy, and don't support the 8-pin connector required to power stronger cards.
I also haven't inspected CyberPowerPC or iBuyPower's home websites because they often have a certain customizable model on sale, and if you choose all the best values in each component field and take all the sensible offers, you can often come away with a 4K-class PC that is cheaper than anything you could get self-building.