Yeah, agree with you in the Intel upgrade path for sure, seems they've stripped down their range, and left little in the way of "steps" in the upgrade path, as for older gen, I do see your point, although I would argue that MS have a lot to do with that, and the fact they wiped an entire generation of old gen out when they tried forcing windows 10 only on new chipsets, effectively forcing older gen stuff off the shelves at the same time, and now, yeah, not much progression so they hold price (was very surprised to not see PCIe 4.0 in the 490 chipsets) Also noticeable is they've stripped away that cheap xeon route that used to be popular, and what's happened to Quad channel memory expansion plans, looks like we're stuck with dual-channel from what I can see, so I do get what you're saying, but at the end of the day, his choice, he wants to stick with intel, so best bang for current buck appears to be that CPU. (don't even get me started on the KF and F variants, why would anyone buy a chip that failed somewhere and was binned lower, for the same money is beyond me)
Coolers cost versus CPU has always been a hot topic, do you change cooler every time you switch CPUs? as you change CPUs be it from one i5 to the next fastest, or step up to an i7 (perhaps increasing TDP) do you overclock less thus creating more heat earlier in your builds life? - then there's the issues of case versus cooler size, I like to get (within reason) a cooler that won't require changing inside 2 upgrades, and thus won't require the case selection revisiting (case options seem so abundant yet so totally sh.t at the same time lately, and wtf is it with all this tempered glass and stupid flashing lights (RGB) everywhere!) - he was looking at/wanting an AIO unit, he picked as you said a brand "hyped" one - i've switched him to one more praised for it's performance rather than name recognition (Arctic Freezer II 280 or if case determines, the 240 model)
The SSD thing we're going to have to agree to disagree on, because you highlighted an example there, that is all but what, £3 cheaper than I can get the evo plus for, and yet is slower in all aspects, does have a goot MTBF value, single sided chipsets on all capacities which is good for heatsink implementation, but is then not the best in power consumption, causing more need for those heatsinks, plus, black friday deals are brining the 970 Pro into his price range or if you want to look at more unorthodox sources they can be picked up for circa 20 more.
I have tweaked his build suggesting he change the RAM for Viper Steel 3600mhz, the Case for the bequiet 601, although if he still wants an optical drive, unknown at this point, then the R6 might be the way to go, or if needs to save cash, stupid as it may sound, the Phanteks Enthoo Pro M although cheaper and a budget case does fit a lot of the variables he'd want, add some dynamat to some of the panels and it'll deaden out some of the sound (although again with the only option left available being the silly full sized glass panel variant!) Motherboard i've guided him to look at the MSI gaming board, although with some shopping around you can get the ASUS at the same sort of price, that said, the mATX MSI Gaming can be had for 30 to 40 pounds cheaper, and have asked if he really needed an ATX sized board.
WiFi was a must, i'm assuming he doesn't want to add a PCIe based card version, or the costs works out more favorable to buy it with it onboard, LAN does finally seem to be moving on (if your other hardware supports it) so I was looking at 2.5GB LAN options
Console not an option, as he wants to use the PC for other stuff, video editing has been mentioned, but how serious i don't know, and that's a whole different playing field, so right now i think he just want's something competent enough to deal with that sort of stuff, whilst allowing son to game.
EDIT:
Forgot to say, with tweaks to his build, i've managed to adjust the available amount of his original budget for the GPU to about £250 - which i think(hope) you'll agree is a much more balanced amount to spend on the GPU in this build, something in the region of a GTX 1660 Super if he want's new or perhaps better if second hand form the members market.
.... now planning a Ryzen 5 3600XT on an MSI x570 Tomahawk, with 32GB of Viper Steel 3600, and a PCIe 4.0 SSD, along with a shift to the Arctic Freezer II 240 cooler