MTS = mounts
STS = Starts
I think everyone has a different take on what weighting to give to the jockey when you're handicapping a race. I personally give much more weight to the trainer than to the jockey, because jockeys have to ride duds for some stables if they want to ride the good ones.
There is no doubt in my mind that there are riders who made victory possible in a close finish, and riders who caused a horse to lose. Even a hall-of-famer can have a bad day and screw up, and a rider whose stats aren't good may be better than the stats show, or may make a sudden improvement in his riding if he learns something.
For me, all I can say is that if everything else about a horse is right, I'll bet the horse no matter who is riding; and if the horse doesn't look to me as if he has a chance, having a "name" rider won't make me bet him.
What you can look for with some stables is jockey changes: see if there's a pattern there, and if there is, if you can turn that to your advantage.
I believe that the trainer has much more to do with the horse's potential to win than the jockey does, so I tend to look at trainer stats, not jockey stats. Sorry if that isn't helpful.