You compared the price per game of someone playing 100 games over 7 years to someone playing 2.5 games per year over 7 years (17.5 games). If dude wants to play 15 big games, plus 85 cheap games (such as most of the games available on Gamepass and PS Now) on Stadia, his average price would be far, far lower. That would be a more reasonable comparison.
Also, Stadia will be available without a monthly subscription. That changes the math substantially.
Finally, even if the average price per game is lower over a seven year period, that doesn't take into account the time value of money. That $500 upfront purchase is a different animal than an occasional outlay for a game, or even a monthly subscription.
Then there's the fact that Stadia doesn't bind one to a console. The Stadia player can fire up his games at his friend's house, in his hotel room, etc. That's a lot harder to do with a console. So, there's really no comparison in terms of convenience. And, as a lifelong gamer myself, this is where I see appeal in streaming services. I don't need to buy consoles for every TV in my house to be able to game in any room. I don't need to miss out on gaming when I'm traveling, etc.
Average price certainly would fall (and he considered 40USD per game instead of 60), but list the 85 games he would buy and price to include in the total amount expended versus PSNow "game netflix".
Money is still money upfront or not, but if you want to make a present value comparison please do it and show us the difference.
The amount you are willing to pay more, get less performance, just for the occasional time you want to play elsewhere is quite different than most people in here.
I'm not willing to pay more for less performance. I am only interested in paying less, or possible about the same amount for more convenience. I see that Stadia (and other streaming services) may allow me to pay less. Right now, I need at least two, preferably three consoles (not different platforms, but three XBs or PSs, for example) to hit most of the places I'd like to play. I wouldn't buy more than one at launch, which makes gaming even less convenient in the short run for me. But, I'd pick up one or two more as prices drop. So, let's say $1000 of consoles over the generation. Then I have a $60 per year subscription to play online. Then I have game purchases on top of that. With Stadia, everything except the game purchase is eliminated. Or, if I want to spend $10 a month for improved performance, it will take 8 years before I spend that $1000 that I would spend on consoles. And, I still save the online game subscription. After all of that savings, I have more convenience gaming too.
I don't know how streaming is going to work out. I plan to continue buying consoles for the foreseeable future. But, I do see that streaming has potential to make gaming much more convenient, and possibly more affordable.
I am also interested to see how Gamepass (and similar services) works cross-gen. I already own two XBones. So, if all games are cross-gen for a while, I could add just once Scarlett on my main gaming TV, then put the bones at the other TVs. That would kind of give me the best of both worlds, without spending a ton of money.