No argument there. Although the Ryzen 2200G/2400G have good enough IGPs to play the lighter games like Dota2, LoL, CS:GO, Overwatch, Fortnite, etc at 1080p low to medium settings. Since an enormous amount of people play those types of games...a dGPU-less PC could still be considered a "gaming" PC.
True statement. The power supplies in OEM PCs are tightly controlled/spec'd to only provide enough watts for the original build.
A powerful CPU and an RTX2080Ti draws about 300W while gaming. A system with a Vega64 GPU draws about 400W. You generally want some headroom to have the PSU running at ~50% duty cycle under those loads, but a good quality 650W PSU is enough for any single-GPU system.
scrampmeyer :
3) Many gaming rigs have upgraded cooling.
Not absolutely necessary, though upgraded CPU cooling does lower temps and/or noise. AMD's Ryzen CPUs come with pretty good stock coolers though (more of an exception to the rule in recent history). Certainly "gaming" PCs could average a higher number of case fans to cope with the added power/heat output of the more powerful hardware inside.
scrampmeyer :
Another thing you want to do when you can is to get as much RAM[as]...you can.
16GB is plenty for today's games (I'd say we're actually between 8GB and 16GB right now...say 12GB average), but yes, RAM requirements always seem to have doubled within the lifespan of the CPU for as long as I can remember. RAM speed is wishy-washy. It does help, but it ranges from negligible to single digit %. Stick with the sweet spot at time of purchase (right now that's DDR4-3000 or DDR4-3200). Also, buy a mobo with 4 ram slots, but get a 2 stick kit of RAM for your initial build. That allows you to add later, rather than replace.