Will,
That was a great post!
While perserverence is not considered a "tool", it might be the #1 most important ingredient.
Best of luck to your "strong minded" son.
The 5 "tools" only give an over view of the players present ability and future potential. There are many areas that are equal or even more important. For example is running a 6.7 60 yards more important than having great instincts and first step quickness?
Some people have what we call "The feel for the game"... Best example to me... Willie Mays. These are the guys who "instinctively" make the right decisions nearly all the time. I believe it's a natural ability and while it can be improved, it can't really be taught.
There are many "two tool" players who have been better than most "four tool" players. The ML is full of them... They're called left fielders and 1st basemen, also DHs in the American League. So for the most part, one fourth (or more) of all positions, could get by with "two + tools". This doesn't mean that all LFs, 1B, DHs can't run, throw or field, it means they are playing because of "two very outstanding tools" and only "two tools". In some cases they're playing with just one outstanding "tool".
When that happens, the one tool is usually "power". There are players in the Big Leagues only because of their ability to hit home runs. Hitting for average and Hitting for power are the only single tools that can get a position player to the Major Leagues in this current era. Of course, as always in baseball, there are a few exceptions to the rule.
Before anyone jumps on it... I am fully aware that Willie Mays was a 5 tool player. Probably the very best 5 tool player ever!