Turkish on 19 September 2017
The biggest difference are:
1. games: Sony never fully supported both handhelds with all of their 1st party might.
2. timing: Switch has the hardware to deliver console graphics at a good enough resolution, neither PSP nor Vita were ready. Most Vita games didn't even run at its native 540p something screen.
3. Another strength of the Switch is its dock mode for TV. The Switch wouldn't nearly be as successful if it didn't deliver a TV experience.
