It's similar to Switch vs. 3DS where the 3DS was aided by early price cuts and revisions to keep it close. On the graph the PS3 already got its €200 and €100 price cuts, so there's nothing major left and it has already fallen behind Switch again.
The difference between the 3DS and PS3 is that the PS3 received a lot more third party support, so it could maintain good sales for a longer time. Switch won't break away from the PS3 with a sharp upwards angle like it did break away from the 3DS, but it's still going to win.
Don't be so sure, the PS3 didn't have competition other than 360, like switch will have now with PS5 and XBX, yes it is not straigh competition 1vs1 but it still is some, and surely when next gen launches it will take some of the future switch sales off of it. Some 20-30% that without next gen would go to the switch.