That is if you only count it for Microsoft games. There are other games in the service, which you could have enjoyed during those times.
For example, kingdom heart is a good series. To some, its not a must buy. But you see kingdom heart 3 on gamepass. Now you multiply it by 300. That is the minimum amount of games the gamepass.
From that, you have the freedom to pick any games you want, and play it for 3 years. In those 3 years, new titles come in and go.
Now to the Playstation side. You have bought 9 games, at the price of those 3 years, which you are keeping it. Now the question is, how many people do you think will go back, and replay it again, after their first gameplay?
9 games in 3 years is pretty low. Considering that is only 3 games per year. And you are stuck playing those 3 games a year, while the other person, went a head, and played a minimum of 3 games a month. 1 good, 2 might be meh. Total of 12 good games, 24 meh for that year.
As for the sales, Demon souls was 61$ last sale on May. It was released with console launch. 7 months of wait time, just for that price.
At the end of the day, 1 gets to keep 9 games for those 3 years, assuming he hasn't bought anything, and doesn't use the discount that much (Sony ps5 discount these days is bad). While the other person went game after game, during those years.
Now let's go back for kingdom heart 3 example. Used copy of that game is 10$ for ps4. Now you are playing 3 times of that game per month. Instead of spending 30$ buying those games, you can spend 25$ a month, testing them out. If you like it, you can buy at discount 20% is when it's leaving the service. So you are spending 8$ for the digital, instead of the cd. Now what happens if you dont like the game. You wasted 10$. You can return the cd, exchange it or sell it for lower price. Or you are stuck at digital, and you can't sell it back. Then, you are losing your money. That 25$ subscription saved you the hassle of wasting that 10$ to buy the game. You could have tried on the service, and jump to other games, if you don't like it.
For game ownership after the service is ending, you are getting xlive free games. They aren't high quality, but its enough to play games, until your next time you want to sub again. In those 3 years, you got 108 games. Some of them might be good. And some of them might be bad. But nevertheless, those are free games you got it for free with the 25$ service.
The only one who doesn't have value, is the one who wants to play new games only. While Microsoft is doing day1 games. Its not guaranteed that person is gonna enjoy it. So the service to him is useless, until they release their 1st party games.
After 3 years and 4 month with the sub, you have 120 games (3*40m) vs 9 games Sony only exclusive. The other games won't have the same quality as Sony games, but they have something to play in the mean time. This if we aren't counting 3rd party game sales, and only going on Sony exclusive vs gamepass only sub, who doesn't buy games.