It's something you have to adapt to. I have <100ms latency on average on my toons - I'm in Phoenix and chose a server located in Los Angeles to minimize lag, but I still get this issue frequently, especially in PVP where target switching may happen in less than a second. It's not a huge issue there if one toon throws a lightning bolt at the wrong target in PVP (unless I was trying to instagib someone) but it can definitely be a problem in PVE.

I have wiped my group countless times in heroics when my alts do not acquire the new target and randomly choose and pull another one. However, I think there is something you can put in your macro to prevent this ("exists,harm" maybe?), but I've been too lazy to research it.