On jumping puzzle and vista
Lag can definitely be a factor in jumping puzzles, but if you have a broadband internet connection you should be fine for just about any sort of JP out there outside of timed ones like the Clock Tower or Skipping Stones. I live in Australia and connect to a US server; my ping is generally around 200 – 300ms, based on past experience in GW1, and I haven’t really had much problems completing any jumping puzzles so far.
If you’re not using a broadband connection because you can’t get one in your area, that’s unfortunate, but it’s out of ANet’s hands.
Poor psycho-motor skills, as you put it, is also a factor that ANet can’t really account for. Some players will be good at JP’s, while others will struggle. During the Halloween event, about 60% of my guild were able to successfully complete the Clock Tower, another 30% just couldn’t manage it despite their best efforts, and the last 10% didn’t bother altogether because they don’t like JP’s. If JP’s are proving to be more frustration than fun, maybe it’s just not an activity that’s meant for you, the same way that PvP or TP power trading may not be fun for other players.