Well then
We have quite a few FAA pilots flying on validation, excluding a some really positive exceptions, most of are unfortunately what Tower Dog so elegantly called "Numb Nuts". Non-standard RT, SOP knowledge is limited, Non standard callouts like instead of "Glideslope Capture" it's Yeah we gliding down the slope or "Gear Down" becomes Dump the gear???? Limited knowledge on meteorology and ICAO procedures and the differences from FAA. I could continue the list on and on, but dont really see the purpose of it. This is not to say that JAA trained pilots do not ever do the same mistakes. Just something I have noted in the past years.
The famed pt121 checkride is no harder nor any easier than an OPC or LPC of a JAROPS1 operator. Standards required by the administrators be it FAA or JAA are about the same. Depending on the airline naturally the standard of training varies. There are some really substandard operators on both sides of the Atlantic and regardless of how good the airline is some goofballs sneak through the system. I recall "Magellan". A Captain that forgot to go to NAV/INS and left it in HDG on 747 while crossing the Atlantic a man that has passed the famed pt121 check with Tower Air! S.hit happens and it could have happened to anyone I guess.
Flyingwise both systems have produced good and bad pilots. But when it comes to the theoretical knowledge of flying and all matters involved, US is far behind the rest of the world and not just JAA. The difference of a Swedish or Nordic or European FO and a US equivalent is marked. There is no doubt that the JAA system as anal as it is, gives a better general knowledge on operating an aircraft than FAA does.
Experience is a totally different matter. You cannot substitue actual experience by reading books. To know something well it must be practiced in real life. However a good general knowledge, thorough theoretical training and eventually experience sounds like a pretty good mix to me.