for the put backs i agree with you, but for the layups and near distance shots my is 1 and 7 guards didn't differ that much, for me the impact of the bigs in your lineup was bigger(at least they had struggle when i played rng with an IS 8 Center).
I think with improving JS you will help your defence lot more, if they had Is it is fine also but i wouldn't train it direct, especially because are also mostly small and the training have not only little impact on the game it also takes very long. If i train guards in big men skills i usually go for Reb and sometimes ID(to make them possible to play SF). And yes maybe you could discuss if the Reb is worth the extra salary, but this is an another topic.